High Field Laboratory

Abstract: Cu-63/65- and Cl-35/37-NMR experiments were performed to investigate triplet localization in the S=1/2 dimer compound NH4CuCl3, which shows magnetization plateaus at one-quarter and three-quarters of the saturation magnetization. In Cu-63/65-NMR experiments, signal from only the singlet Cu site was observed, because that from the triplet Cu site was invisible due to the strong spin fluctuation of onsite 3d spins. We found that the temperature dependence of the shift of Cu-63/65-NMR spectra at the singlet Cu site deviated from that of macroscopic magnetization below T=6 K. This deviation is interpreted as the triplet localization in this system. From the Cl-35/37-NMR experiments at the 1/4-plateau phase, we found the two different temperature dependences of Cl shift, namely, the temperature dependence of one deviates below T=6 K from that of the macroscopic magnetization as observed in the Cu-63/65-NMR experiments, whereas the other corresponds well with that of the macroscopic magnetization in the entire experimental temperature region. We interpreted these dependences as reflecting the transferred hyperfine field at the Cl site located at a singlet site and at a triplet site, respectively. This result also indicates that the triplets are localized at low temperatures. Cu-63/65-NMR experiments performed at high magnetic fields between the one-quarter and three-quarters magnetization plateaus have revealed that the two differently oriented dimers in the unit cell are equally occupied by triplets, the fact of which limits the theoretical model on the periodic structure of the localized triplets.

Abstract: Formation peculiarities of the static thermo-electric modes that may be observed in high temperature superconductors at the DC current are studied taking into consideration the temperature-decreasing dependence of the power exponent (n-value) of the voltage-current characteristic of a superconductor. The used models are based on the steady zero-dimensional models. The study is made for the conduction-cooling and liquid coolant conditions at different operating temperatures. It allows us to investigate the non-isothermal voltage-current characteristic of Bi2223 and YBCO that rooted the development of their stable and unstable thermo-electric regimes. It is shown that the temperature dependence of an n-value may lead, first, to usually observed static voltage-current and temperature-current characteristics having one stable and unstable parts and, second, to unexpected thermo-electric states in the temperature range that is closed to its transition into the normal state. It is a result of the formal temperature variation of the differential resistivity of a superconductor depending on its temperature-decreasing critical current density and n-value. As a result, to describe correctly thermal stability conditions and analyze theoretically the quench processes in high temperature superconductors, the temperature dependences of their critical current density and n-value must be restored before the transition of a superconductor into the normal state as carefully as possible. (C) 2009 Elsevier Ltd. All rights reserved.

Abstract: The results of a comprehensive study of the structural, magnetic, and magnetotransport properties of the Heusler compounds Ru2-xFexCrSi are presented. The Fe-rich compounds (x >= 1.5) exhibit a usual ferromagnetic transition. The Ru-rich compound (x=0.1) does not show ferromagnetism but exhibits a peak in magnetic susceptibility at T-N(*)=30 K. Nevertheless, specific-heat measurements show that there is no antiferromagnetic transition at T-N(*) nor at any other temperatures. With further decreasing temperature strong irreversible behavior occurs below a temperature T-g. It is proposed that these results can be interpreted as successive spin-glass transitions at T-N(*) and T-g. The compounds with intermediate x (=0.3 and 0.5) are found to be ferromagnetic. Both the saturation magnetization and the Curie temperature T-C increase with increasing x. However, being different from the Fe-rich compounds, hysteresis of the magnetization is observed and this suggests that the ferromagnetism has glassy character. In lower-temperature range fairly large negative magnetoresistance are observed. These results are suggestive of a magnetically inhomogeneous ferromagnetic state, that is, the formation of ferromagnetic clusters.

Abstract: In order to understand the vortex pinning properties by the BaZrO3 (BZO) and BaSnO3 (BSO) nano-rods in Er123 films, the microstructure and the angular dependence of J(c) and resistivity were measured in detail for the BZO and the BSO added Er123 films with the similar matching field prepared by pulsed laser deposition. We found that the peak at B//c in the angular dependence of J(c) for the Er123 film with BSO nano-rods was higher in a wide magnetic field region up to the irreversible field than that for the Er123 film with BZO nano-rods, although the minimum values of the angular dependence of J(c) are similar each other. Hence, the BSO nano-rods work more effectively as the c-axis-correlated pinning center than the BZO nano-rods because of the different elementary pinning energy of nano-rods.

Abstract: Study of magnetostriction of (Lu0.8Ce0.2)(2)Fe-17 has been performed by two methods, bulk and microscopic: by the capacitor dilatometer on a single crystal grown by the Czochralski method and by the X-ray powder diffraction. The field-induced transition from the antiferromagnetic to the ferromagnetic state is accompanied by the lattice expansion both in the basal plane and along the c-axis of the hexagonal structure. In addition to the spontaneous linear magnetostriction lambda(s)(a) = 0.8 x 10(-3), lambda(s)(c) = 6.8 x 10(-3) along the a and c axes, respectively, and volume effect omega(s) = 8.4 x 10(-3), a comparable field-induced magnetostriction (lambda(a) = 1.3 x 10(-3), lambda(c) = 3.4 x 10(-3), omega = 6.0 x 10(-3)) is observed in a field of 5T applied along the a-axis. (C) 2008 Elsevier B.V. All rights reserved.

Abstract: Phthalocyanine-doped MgB2 tapes were prepared by the in situ powder-in-tube method. The relationships between the critical current properties, crystallinity and microstructure were studied as a function of the phthalocyanine doping level. It is found that both H-irr and H-c2 were improved when MgB2 samples were doped with phthalocyanine, which are mainly attributed to the effective carbon substitution and enhanced flux pinning strength caused by very fine grain sizes. Furthermore, compared to pure samples, the MgO content remained almost unchanged in all doped tapes, which is very beneficial to having better grain connectivity in MgB2. Significantly improved J(c) was obtained in the phthalocyanine-doped MgB2 tapes, especially under high magnetic fields.

Abstract: The microstructure and superconducting properties of Bi-based superconducting tapes fabricated in high magnetic fields were investigated. The flat tapes 0.6 mm in thickness and 3 mm in width set on the an isolite holder were sintered at 835-850 degrees C for 120 h in 0 or 10 T magnetic field in air. The results show that the tape sintered with 10 T magnetic field shows stronger c-axis alignment of the Bi-2223 phase and higher J(c) value than that sintered without magnetic field. The tape sintered at 835 degrees C in a 10 T magnetic field shows a high proportion of Bi-2223 phase, however, a low c-axis alignment of the Bi-2223 phase. The tape sintered above 845 degrees C in a 10 T magnetic field shows a strong c-axis alignment of the Bi-2223 phase, however, a low proportion of Bi-2223 phase. The tape sintered at 840 degrees C in a 10 T magnetic field shows a strong c-axis alignment of the Bi-2223 phase, a high proportion of Bi-2223 phase, and the highest J(c) value. (C) 2009 Published by Elsevier B.V.

Abstract: Correlation of phase formation, critical transition temperature T-c, microstructure, and critical current density J(c) with sintering temperature has been studied for acetone doped MgB2/Fe tapes. Sintering was performed at 600-850 degrees C for 1 h in a flowing At atmosphere. High boron substitution by carbon was obtained with increasing the sintering temperature; however, the acetone doped samples synthesized at 800 degrees C contain large size MgB2 grains and more MgO impurities. Incomplete reaction for the acetone doped samples heated at 600 degrees C result in bad intergrain connectivity. At 4.2 K, the best J(c) value was achieved in the acetone doped sample sintered at 700 degrees C, which reached 24,000A/cm(2) at 10 T and 10,000A/cm(2), at 12 T, respectively. Our results indicate that the small grain size and less impurity were also important for the improvement of J(c)-B properties besides the substitutions of B by C. (C) 2008 Elsevier B.V. All rights reserved.

Abstract: X-ray powder diffraction, magnetization measurements, and differential thermal analysis (DTA) of polycrystalline MnBi were carried out in zero magnetic field as will as in magnetic fields of up to 14 T and in the temperatures range of 300-773 K, in order to investigate magnetic phase transition. In zero magnetic field, a magnetic phase transition from ferromagnetic to paramagnetic state is exhibited at temperature (T-t) of 628 K, accompanied by decomposition. With increasing magnetic field up to 14 T, T-t increases linearly with the rate of 2 KT-1. A metamagnetic transition between the paramagnetic and field-induced ferromagnetic states was observed just above T-t The exothermic and endothermic peaks were detected in the magnetic field dependence of DTA signals in the interval of 626-623 K, which relates to the metamagnetic transition. The obtained results are discussed on the basis of a mean field theory.

Abstract: MgB2 was thought as a promising superconductor used at temperatures around 20 K for cryogen-free magnet. Nanostructure materials were often selected as MgB2 additives due to their high chemical reactivity. In this paper, the mixture of nano-C and nano-SiC was doped to MgB2 bulks and tapes. The co-doping effect of C and SiC on the phase formation, microstructure, and critical current density of MgB2 bulks and tapes were systematically investigated. The mechanisms for the superconducting properties improvement in co-doped MgB2 superconductor was analyzed based on the characterization and measuring results.

Abstract: The ab-plane infrared and optical reflectance of single-crystal Bi2Sr2CoO6+delta (0.4 <delta < 0.5) have been measured over a wide frequency range (50-55000 cm(-1)) and at temperatures between 20 and 330 K. The room-temperature infrared spectrum displays an insulating characteristic. The optical gap determined from the infrared conductivity (similar to 0.53 eV) is consistent with thermal activation energy from dc transport measurements. Upon passing through the 265 K antiferromagnetic ordering transition, a softening of the phonon mode near 205 cm(-1) correlates well with the temperature-dependent normalized square of the sublattice magnetization. Furthermore, the magnetic-order-induced splitting of the phonon modes at about 238 and 376 cm(-1) is observed. Additionally, the phonon mode at about 588 cm(-1) exhibits a Fano-type line shape. Since no appreciable structural change was detected at low temperatures in x-ray diffraction studies, all of these observables suggest a complex nature of spin-phonon coupling in this material.

Abstract: A magnetic field of 12 T was applied during the annealing of amorphous alpha-Fe2O3 microspheres. The authors demonstrate that magnetic field processing leads to the formation of gamma-Fe2O3 phases in the microspheres, and the field-treated microspheres exhibit typical room-temperature ferromagnetic behavior, whereas non-field-heated sample presents paramagnetism. The improvement in magnetic propertiesis considered to be a result of magnetic field-induced transformation from alpha-Fe2O3 to gamma-Fe2O3. (C) 2009 Elsevier B.V. All rights reserved.

Abstract: We have characterized current transport properties in a GdBa2Cu3O7-delta coated conductor fabricated by a combination of ion-beam assisted deposition (IBAD) method and pulsed laser deposition (PLD) method with reel-to-reel systems, and have applied them to a coil design for a high-field magnet. The J-E characteristics in the conductor are given as a function of temperature, magnetic field and the field angle based on percolation transition model, and its potential as a high-field magnet coil is discussed based on a finite element method analysis. As a result, we have found that the conductor with l(c) = 350 A/cm-w at 77 K and self-field has a possibility to realize a 40 T magnet coil with very compact size (300 mm in outside diameter) and small usage of the coated conductor (8 km). Furthermore, we have also investigated the relationship between the scale of the magnet coil and the corresponding requirements for the conductor. Consequently, it has been suggested that the improvement of critical current characteristics of the conductor greatly advances the downsizing of the coil without large increment in hoop tensile force. In addition, it has also been found that such downsizing of the coil contributes to the reduction in stored energy and total magnetization loss of the coil. This means that the recent improvement of critical current characteristics in coated conductors is especially worthwhile for high-field magnet coils in terms not only of downsizing but also of quench protection and magnetizing/demagnetizing operation. (C) 2009 Elsevier B.V. All rights reserved.

Abstract: Multilayered MgB2/Ni thin films on Si substrates by electron beam evaporation were fabricated to enhance the critical current density J(c) in magnetic fields parallel to the surface. The magnetic field dependence of J(c) of the multilayered MgB2/Ni thin films for B//surface shows a peak at the matching field. In the field angular dependence of J(c), a sharp peak appears at B//surface. These results indicate that Ni layers which have ferromagnetism act as two-dimensional pinning centers in multilayered MgB2/Ni thin films. The vortex glass-liquid transition temperature T-g and the pinning parameter m were evaluated from the E-J characteristics. The slope of the magnetic field dependence of m in the multilayered MgB2/Ni thin film under the matching field is larger than that over the matching field. In the T-g/T-c-B phase diagram, the remarkable enhancement of T-g for B//surface appears around the matching field. These features are characteristic behaviors for two-dimensional pinning centers. (C) 2009 Published by Elsevier B.V.

Abstract: The minimum quench energy (MQE) and normal zone propagation velocity (NZPV) of three kinds of Nb3Al superconductors fabricated by the rapid heating, quenching and transformation (RHQT) process were measured under various conditions of applied magnetic field (10-14 T), temperature (7-11 K), and transport current (80-95% of the critical current), while cooled by a cryocooler for developing the over 20-T class cryogen-free magnet. As a result, MQE values were related to the critical current density (J(c)); high MQE was obtained for low J(c). It is assumed that J(c) has a stronger influence on the MQE than specific heat, thermal conductivity, resistivity, and other parameters of the composite superconductor including the matrix and the stabilizer. NZPV was mainly proportional to the transport current density varying with applied field and temperature. The second contribution to NZPV is assumed to be heat capacity depending on the wire configuration.

Abstract: In order to study the degradation of critical temperature T-c for a coated conductor using nanorods, the relationship between Tc and nanorod shape was investigated by transmission electron microscopy for ErBa2Cu3Oy (Er123) films with BaZrO3 (BZO) and BaSnO3 (BSO) nanorods. The dependence of Tc on the BZO or BSO content was different, however, the nanorods interface density dependence of Tc was the same for both. Thus, the interface density of the nanorods controls Tc of the nanorod-added films. The different degradation in Tc between the BZO and BSO nanorod-added films originated in differences in the nanorod diameter and density. (C) 2009 The Japan Society of Applied Physics

Abstract: We report the effect of acetone addition on in situ powder-in-tube processed MgB2/Fe tapes by using acetone as liquid additive. The amount of acetone was varied from 0 to 15 wt.%. We found that a significant J (c)-B enhancement was easily achieved in high field by acetone doping. At 4.2 K, the transport J (c) for the best acetone added tapes (5 wt.%) reached up to 2.4x10(4) A/cm(2) at 10 T. With increasing acetone concentration, the a-axis lattice parameters, B (c2) and B (irr), were not much changed; however, the insulating MgO impurities and pores gradually increased, thereby resulting in the obvious decrease of J (c) values for 10 and 15 wt.% acetone-added samples, especially within low field region.

Abstract: We have characterized nonlinear current transport properties in a coated conductor as a function of temperature, magnetic field vector and mechanical strain, and then have developed a thermally-electromagnetically-structurally coupled analysis code for a high-field magnet coil. The distributions of heat generation and electromagnetic force in the coil are computed by electromagnetic analysis. Then, the temperature distribution and the strain distribution are correspondingly calculated by thermal analysis and by structural analysis. Furthermore, both of them are fed back to the electromagnetic analysis. These analyses are based on finite element method, and are repeated until the convergence. By taking a design example of a 40 T class magnet coil using a GdBCO coated conductor, we have discussed the necessity of the consideration of thermally-structurally influenced transport properties in the coil for the coil design.

Abstract: We have been developing high-strength Nb3Sn strand cables to construct a high-field superconducting outsert for a 45 T hybrid magnet with a 25 T water-cooled resistive magnet. Evidence for cold work strengthening of repeated bending treatment (prebending effect) on Nb3Sn strands internally reinforced with CuNb stabilizer, which exhibits significant enhancement of the critical current density, has been found in the superconducting magnet fabrication process using a react-and-wind method. The strand cables were designed by controlling the constituent number of CuNb/Nb3Sn strands with the prebending effect and stainless steel strands, which are expected to have a stress limit 580 MPa at 0.4% strain. In order to design a compact superconducting outsert, high-strength strand cables are adopted in a magnetic field region below 14 T to maintain relatively large engineering current densities (J(e)). In a higher-field region above 14 T, YBa2Cu3O7 (Y123) coated conductors are employed for an insert coil. Using combination of Y123, Nb3Sn and NbTi superconductors, a 20 T superconducting outsert with a room temperature bore of 400 mm consisting of three layers made of Y123, two layers of CuNb/Nb3Sn and two layers of NbTi was designed. The coil parameters are 440 mm inner diameter, 1080 mm outer diameter and 1138 mm coil height. A very compact 20 T superconducting outsert with a stored magnetic energy 72 MJ at an operation current 903 A can be developed for a 45 T hybrid magnet.

Abstract: A 7-strand Nb3Sn superconducting cable, which consists of three pre-bent CuNb/Nb3Sn strands, three stainless-steel (SS) strands, and a center SS strand, was fabricated. 2.5 turns of the cable was wound on a 262-mm diameter GFRP bobbin A triplet consisting of three pre-bent CuNb/Nb3Sn strands was also tested for comparison. The reinforcement effect of stainless-steel strands in a cable was investigated to develop a high-strength large-current superconducting cable. The hoop stress test result indicated that the stainless-steel reinforced CuNb/Nb3Sn cable showed better performance than the CuNb/Nb3Sn triplet under the hoop stress, because the stainless-steel strands reduced the hoop stress on Nb3Sn strands. Furthermore, the solder impregnation of the cable, which made the seven strands a monolithic conductor, improved its performance.

Abstract: A system was developed measuring x-ray powder diffraction in high magnetic fields up to 5 T and at temperatures from 283 to 473 K. The stability of the temperature is within 1K over 6 h. In order to examine the ability of the system, the high-field x-ray diffraction measurements were carried out for Si and a Ni-based ferromagnetic shape-memory alloy. The results show that the x-ray powder diffraction measurements in high magnetic fields and at high temperatures are useful for materials research.

Abstract: The introduction of the c-axis-correlated disorder is a promising technique for the improvement of the critical current density J(c) for B // c of REBa2Cu3Oy (RE123) films and tapes. In order to understand the vortex pinning mechanism with the different variety of the c-axis-correlated disorder, the angular dependence of J(c) was measured in detail for an Y123 film with BaZrO3 nano-rods, a Sm123 film with fine nano-particles and edge dislocations and an Y123 film with columnar defects introduced by the heavy-ion irradiation parallel to the c-axis. We found that the vortex pinning state for the variety of the c-axis-correlated pinning is similar in low fields below the matching field, but it shows different behaviors in high fields above the matching field. It is considered that the interstitial vortices interacted with the c-axis-correlated disorders through the vortex interaction may play an important role for the appearance of the c-axis-correlated pinning behavior in a high-field region above the matching field. (C) 2008 The Japan Society of Applied Physics.

Abstract: Magnetization measurements were performed on a DyB2C2 single crystal under pressures up to 1.0 GPa in high magnetic fields up to 26 T. At 4.2 K, pressure-induced magnetic phases are found below 8 T along the [1 0 0] axis, which varies for pressures and temperatures. (C) 2007 Elsevier B.V. All rights reserved.

Abstract: Activated carbon doped MgB2 tapes were prepared by the in situ powder-in-tube method. The phase, crystal structure, microstructure, resistance, etc were analyzed by x-ray diffraction (XRD), scanning electron microscopy (SEM) and a physical properties measurement system (PPMS). It was found that the irreversibility field (H-irr) and upper critical field (H-c2) were enhanced when MgB2 samples were doped with activated carbon, and the magnetic field dependence of the critical current density (J(c)) was improved significantly. For the 5% activated carbon doped MgB2 tapes, the J(c) value was nearly eight times higher than that of undoped tapes at 13 T (4.2 K). On the other hand, the activated carbon doping level has a significant effect on the J(c) values of MgB2 tapes. When the doping level is higher than 5%, the J(c) values decrease with increasing activated carbon doping level.

Abstract: The tensile strain dependence of the upper critical field B-c2 for Nb3Sn wires was measured using a new apparatus for applying tension at low temperature. The critical current I-c calculated from the strain-dependent B-c2 measurements is the almost consistent with the measured I-c. In the measurements by a new apparatus, the axial and the lateral applied strains were examined by the strain gauges attached onto the wire. The deviatoric strain epsilon(dev) and the hydrostatic strain epsilon(hyd) were estimated by the axial and the lateral strain. We found the deviatoric strain dependence of B-c2 is different between the tensile and compressive strain states. This means that the hydrostatic strain also should be taken into account in order to understand the strain effects on the superconducting properties of Nb3Sn.

Abstract: In order to investigate the pressure effect on electrical properties Of CuV2S4, We performed the electrical resistivity measurements under high pressures up to 8 GPa for a high-quality polycrystalline sample. The charge density wave (CDW) transition temperatures increase with increasing pressure. The residual resistivity rapidly increases with increasing pressure over 4 GPa, and the temperature dependence of the electrical resistivity at 8 GPa exhibits a semiconducting behavior below about 150K, indicating that a pressure-induced metal-insulator transition occurs in CuV2S4 at 8 GPa. (C) 2007 Elsevier B.V. All rights reserved.

Abstract: In this work we focus on the microstructural and magnetic characterization of CuNb/Nb3Sn wires with different architectures (design and reinforcement). The microstructural characterization was performed using scanning electron microscopy. AC magnetic susceptibility was measured with field applied both parallel and perpendicular to the wire axis. The heat treatment performed to form the A-15 superconducting phase leads to partial spheroidization followed by coarsening of the Nb filaments in the reinforcement material. The differences concerning the microstructure of the reinforcement material among the investigated wires were reflected in the broadening of the superconducting transition of Nb, more evident for a field applied parallel to the wire axis. From the magnetic data the wires were also compared in terms of the superconducting volume fraction.

Abstract: Transport characteristics of IBAD/CVD-YBa2Cu3O7 (YBCO) coated conductor were measured at 4.2 K under hoop stress. The conductor was fabricated by a multi-stage metal-organic chemical vapor deposition (CVD) method. The YBCO layer was deposited on Hastelloy substrate with PLD-CeO2 and IBAD-Gd2Zr2O7 buffer layers. A 20-mu m silver layer was sputtered as a protective and stabilizing layer. The hoop stress test coils were fabricated by winding the conductor on a 250-mm diameter stainless-steel bobbin by five turns. Two coils, denoted as coils A and B, were fabricated. The Hastelloy substrate located outside for coil A and inside for coil B. Both coils were tested in magnetic field at 4.2 K under hoop stresses. Coil A and B experienced 1028 and 777 MPa at 11 T, 4.2 K. The measured stress-strain curves provided that the Young�s modulus of the conductor was 190 GPa. The tolerable stress of similar to 1000 MPa and the Young�s modulus of 190 GPa are consistent with the values obtained by a tensile test. The hoop stress test results indicates that the YBCO coated conductor is promising for application under huge hoop stress.

Abstract: Magnetic and electrical resistivity changes due to a martensitic transformation in large magnetic fields were investigated in a NiCoMnIn alloy. The transformation is interrupted at about 150 K during field cooling and does not proceed with further cooling. The obtained two-phase condition is frozen at low temperatures and zero field heating releases this condition, inducing a �forward� transformation. These unusual phenomena can be explained by an abnormal behavior in the transformation entropy change and an extremely low mobility of the phase interfaces detected at low temperatures. (c) 2008 American Institute of Physics.

Abstract:

Abstract: The Tsukuba Magnet Laboratory (TML) and the High Field Laboratory for Superconducting Materials collaborated on the design study of a 50 T-class hybrid magnet. The highest fields of the hybrid magnet were examined with the existing 15 MW DC source at the TML used for the resistive insert magnet. The strength of the Cu-Ag wire exceeds 1400 MPa in ultimate tensile strength (UTS). Several upper-design stresses corresponding to the Cu-Ag wire strength were placed on Bitter disks to evaluate the resistive insert. The design was conducted with two inner radii, 29 mm and 19 mm. Resistive insert magnets are consist of three-layered coaxial Bitter coils operated with the 20 T outer superconducting magnet with a room temperature bore of 0400 mm. In this hybrid magnet, a UTS of 1200 MPa is needed for the Bitter disks of the resistive insert to generate 46 T.

Abstract: The homogeneity range of U2Co17-xSix system with the hexagonal Th2Ni17-type crystal structure extends from x= 1 to 3.4. The variation of the magnetic properties within the homogeneity range was studied on single crystals. All the compounds are ferromagnetic, M-s, and T-C decrease monotonously with increasing Si content. The strongly modified magnetic anisotropy of U2Co17-xSix, as compared to isostructural Lu2Co17-xSix with the non-magnetic Lu, points to a magnetic state of U up to x = 3.0. The U contribution to K, decreases with increasing Si content and vanishes at x = 3.4 that can be treated as a transition from magnetic to non-magnetic state of U. Spin reorientation was observed with varying temperature in compounds with x <= 3 due to a competition of the U and Co sublattices anisotropies which occurs as two second-order phase transitions of the �plane-cone� and the �cone-axis� type. (c) 2006 Elsevier B.V All rights reserved.

Abstract: We have succeeded in synthesizing the Heusler compounds Ru2CrGe and Ru2CrSn and performed magnetization measurements in high magnetic fields up to 18 T in order to investigate the magnetic properties of Ru2CrGe and Ru2CrSn. We confirmed that the compounds have an ordered Heusler L2(1) structure. It was found that Ru2CrGe is an antiferromagnet with the Neel temperature T-N = 13 K and Ru2CrSn shows a spin-glass-like behavior below 7 K. The Heisenberg exchange constants determined on the basis of the experimental results for Ru2CrGe are different from the values of Mn-based Heusler compounds. (C) 2008 American Institute of Physics.

Abstract: A superconducting multilayer coil using CuNb/ Nb3Sn wire was fabricated by the pre- bent react- and- wind ( R& W) method. The pre- bent R& W method is a combination of the pre- bending treatment and the conventional R& W process. A 0.8% pre- bending strain was applied by ten fixed pulleys. The coil was tested in magnetic fields of 14, 12, 11 and 10 T at 4.2 K. The coil quench current achieved 100% load ratio of the short sample critical current in the 14 T back- up field. The quench current of the outer section coil achieved 100% of the short sample critical current in the 12 T back- up field. The coil quench currents in various magnetic fields are discussed from a hoop stress and mechanical disturbance point of view.

Abstract: Correlation of phase purities, microstructure, J(c) and H-c2 with sintering temperature has been studied in Zn-stearate-doped MgB2/Fe tapes. All doped tapes show significant enhancements in J(c) and H-c2. TEM analyses revealed that strong flux pinning centers induced by grain boundaries and crystal defects as well as carbon substitution effect are responsible for the improvement of J(c) and H-c2 values. Although a high sintering temperature of 850 degrees C increases the grain size, improved grain connection can compensate for this disadvantage, giving the best J(c) of 2.0 x 10(4) A cm(-2) at 4.2 K and 10 T. On the other hand, tapes sintered at 900 degrees C have a lower J(c) due to the larger grain size and more MgO impurities.

Abstract: In oder to obtain a high- density magnetic recording medium using an L1(0) ferromagnetic ordered alloy, it is imperative to make its c- axis perpendicular to the thin film. In this work, we have investigated experimentally the c- axis orientation process of the L1(0) FePt in nanostructured FePt/ B2O3 thin films, and its orientation mechanism is proposed on the basis of the micromechanics concept. From our present experimental results, we have found that there are three characteristic features when such c- axis orientation occurs in the thin films: the marked crystallographic orientation occurs during the cooling process, the axial ratio c/ a experimentally observed tends to be considerably lower than the equilibrium value, and the degree of c- axis orientation is lowered for a relatively thick film, that is, the plane- stress state plays a key role to make the c- axis perpendicular to the film surface. In- plane ( biaxial ) tensile stresses are considered to be yielded due to the thermal shrinking difference between the two materials, and ordered FePt particles with the c- axis perpendicular to the film surface is considerably stabilized under such in- plane tensile stresses in terms of the mechanical interaction energy. The validity of this mechanism is also confirmed for CoPt/ B2O3 thin films.

Abstract: The concentration evolution of crystal structure, magnetic moment and anisotropy constants in U-2(Fe1-xNix)(13.6)Si-3.4 investigated on single crystals grown by the Czochralski method is found to be similar to that in the previously studied U-2(Fe1-xNix)(13.6)Si-3.4 system, only the Ni solubility is limited by x = 0.3 in difference with unlimited Co solubility. (c) 2007 Elsevier B.V. All rights reserved.

Abstract: The magnetostriction and magnetoresistance associated with the field-induced and spontaneous first-order antiferro-ferromagnetic (AF-F) phase transitions have been studied for quasi-single-crystalline samples of La0.25Sm0.75Mn2Si2, La0.25Y0.75Mn2Si2 and La0.27Y0.73Mn2Si2 compounds with natural layered ThCr2Si2-type structure. It was found that both the spontaneous and field-induced AF-F transitions are accompanied by a large volume magnetostriction Delta V/V approximate to 2 x 10(-3) and anisotropic linear changes of the lattice parameters Delta a/a approximate to 1.6 x 10(-3), Delta c/c approximate to -0.75 x 10(-3). The field-induced AF-F magnetic phase transition has been observed in magnetic fields applied both along the c-axis and in the basal plane, and the magnetostriction value is virtually independent of the direction of applied field. It has been found also that the magnetoresistance is positive in these compounds (the value of the electrical resistance in the ferromagnetic state is higher than that in the antiferromagnetic state) for the fields applied both along the c-axis and in the basal plane. The value of the magnetoresistance observed along the c-axis is 30 times as high as that in the basal plane. The obtained results indicate that the electronic band structure changes are likely responsible for the AF-F magnetic phase transitions observed in the RMn2X2 compounds.

Abstract: The effect of the starting composition on the superconducting properties for ternary system (Nd, Sm, Gd)-Ba-Cu-O filaments was systematically investigated. The filaments with the composition of (Nd-0.33,Sm-0.33,Gd-0.33)(1.18)Ba2.12Cu3.09Oy (sample A), (Nd-0.50,Sm-0.25,Gd-0.25)(1.18)Ba2.12Cu3.09Oy (sample B), (Nd-0.25,Sm-0.50,Gd-0.25)(1.18)Ba2.12Cu3.09Oy (sample C) and (Nd-0.25,Sm-0.25,GdO.50)(1.18)Ba2.12Cu3.09Oy (sample D) were prepared by a solution spinning method. All samples partially melted at temperature range of 1030-1080 degrees C in flowing 0.1% O-2 + Ar exhibited J(c) value higher than 10(4) A/cm(2) at 77.3 K and self-field. Among these samples, the best transport J(c) value of 7.2 x 10(4) A/cm(2) was attained in sample B with Nd-rich composition. The field dependence of transport J(c) value was also examined at various temperatures between 77.3 K and 90 K in applied magnetic fields up to 17 T. In the case of samples A. the J(c) value gradually decreased with increasing the applied magnetic field, and the J(c) value of 2.4 x 10(3) A/cm(2) at 77.3 K was maintained up to high magnetic fields of 17 T. On the contrary, the Jc value of sample B decreased with increasing the applied magnetic field and the superconductivity disappeared at about 15 T. It was found that the three element ratio in NSG123 contributed to flux pinning in a different manner and affected in J(c) behavior in magnetic field. (c) 2008 Elsevier B.V. All rights reserved.

Abstract: In order to investigate the effect of fabrication process on the superconducting properties of MgB several types of MgB2 tapes were fabricated using different techniques, such as different deformation ratio, ratio, different precursor process, etc. It is found that the higher rotary-swage ratio, the better J(c)-B properties. For example, at 4.2 K and 10 T,J(c) value for the samples swaged to 4 mm was five times higher than that for the samples swaged to 6 mm. On the other hand, the J(c) values were significantly improved when the staring powder was homogenized by ball milling. For instance, at 10 T (4.2 K), the J(c) value was improved from 2.2 x 10(3) A/cm(2) to 3.5 x 10(3) A/cm(2) for undoped samples sintered at 800 degrees C, while it was improved from 1.3 x 10(4) A/cm(2) to 1.8 x 10(4) A/cm(2) for 5 at% carbon doped ones. Detailed mechanism of the J(c)-B property difference induced by different deformation ratio or different staring material process is discussed based on the systematically examined results. (c) 2008 Elsevier B.V. All rights reserved.

Abstract: We report the electric conductivity of three-dimensional (3D) nanoporous gold at low temperatures and in strong magnetic fields. It was found that topologically disordered 3D nanoporosity leads to extremely low magnetoresistance and anomalous temperature dependence as the characteristic length of nanoporous gold is tuned to be similar to 14 nm. This study underscores the importance of 3D topology of a nanostructure on electronic transport properties and has implications in manipulating electron transport by tailoring 3D nanostructures.

Abstract: We set out to design as compactly as possible a 30 T superconducting magnet consisting of an YBa2Cu3O7 (Y123) insert coil and a CuNb-reinforced Nb3Sn (CuNb/Nb3Sn) background coil. The engineering current density J(e) for an Y123-coated conductor tape is larger at 1415 T and 4.2 K than that for a CuNb/Nb3Sn strand. Adopting Y123-coated conductor tapes in the high field region above 14-15 T proves highly effective for the fabrication of a very compact 30 T superconducting magnet. A 30 T, 52 mm-room-temperature bore superconducting magnet can be constructed in the coil grading of a 16T Y123 insert and a 14T CuNb/Nb3Sn background coil, and the stored magnetic energy of 32MJ successfully lies in the 1/3 level in comparison with the 30T nuclear-magnetic-resonance (NMR) superconducting magnet reported previously. (c) 2008 The Japan Society of Applied Physics

Abstract: The High Field Laboratory for Superconducting Materials (HFLSM) and the Tsukuba Magnet Laboratory (TML) conducted in collaboration a case study on development of a 50 T-class hybrid magnet. To construct a high magnetic field magnet with compact and energy-saving design as well as with easy operation and maintenance, one has to develop high-strength Nb3Sn strand cables, with maximized superconducting characteristics and which can withstand a large electromagnetic force over 500 MPa. For this purpose, the HFLSM has proposed and investigated the effect of repeated bending treatment (prebending) on Nb3Sn strands internally reinforced with CuNb stabilizer leading to significant enhancement of the critical current density. In this report we present our results on application of the prebending effect to the development of high-strength strand cables. The designed prebent-strand cables are composed of three CuNb/Nb3Sn strands (3 x phi = 1.73 mm) and four stainless steel strands (4 x phi = 1.73 mm). High-strength CuNb/Nb3Sn strand cables have shown a stress limit of 552 MPa at 0.4% strain, and a critical current of I-c = 1000 A at 18.5 T and 2.0 K. For such high-strength strand cables, a 20 T superconducting magnet with a room temperature bore (phi = 400 mm) consisting of five layers made of CuNb/Nb3Sn and two layers of NbTi was designed. The coil parameters are: inner diameter phi = 440 mm, outer diameter phi = 1332 mm, coil height 1321 mm, inductance 350 H and magnetic stored energy 144 MJ at 908 A of the operation current. Winding of the coil was experimentally successfully simulated using dummy 3 + 4 strands cable composed of three Cu strands and 4 stainless steel strands with a similar design to the 3 + 4 strands superconducting cable presented above. The 20 T superconducting coil will be used as a 20 T outsert for a 25 T water-cooled resistive insert to obtain a 45 T hybrid magnet.

Abstract: We have performed photoemission spectroscopy studies of single-crystal line CuV2S4 using synchrotron radiation, in order to clarify the electronic structure changes across the charge density wave (CDW) transitions in a spinel type compound. Photo-energy-dependent studies show a peak Just below the Fermi level (E-F), structure which undergoes resonant enhancement at an excitation energy hv = 54.5 eV. This energy corresponds to the V 3p-3d threshold energy, thus suggesting that the density of states (DOS) at EF is mainly composed of V 3d states. From temperature-dependent measurements, we observe a reduction in spectral DOS at and near EF, leading to the formation of a pseudo-gap across CDW transition temperatures. The pseudogap energy scale of similar to 0.05 eV, identified at the top of the valence band, is significantly larger than the value expected from a BCS-like transition.

Abstract: A significant enhancement of critical current density (J(c)) and H-irr in MgB2 tapes has been achieved by the in situ powder-in-tube method utilizing hollow carbon spheres (HCS) as dopants. At 4.2 K, the transport J(c) for the 850 degrees C sintered samples reached 3.1 x 10(4) and 1.4 x 10(4) A cm(-2) at 10 and 12 T, respectively, and were better than those of optimal nano-SiC-doped tapes. The effects of different sintering temperature on lattice parameters, amount of carbon substitution, microstructure and J(c) of doped samples were also investigated. These results demonstrate that HCS is one of the most promising dopants besides nano-carbon and SiC for the enhancement of current capacity for MgB2 in high fields.

Abstract: Magnetic resonance imaging with high static magnetic fields (SMFs) has become widely used for medical imaging purposes because SMFs cause fewer genotoxic side effects than ionizing radiation (IR). However, the effect Of exposure to high SMFs on global transcription is little understood. We demonstrate that genes involved in motor activity, actin binding, cell adhesion, and cuticles are transiently and specifically induced following exposure to 3 or 5 T SMF in the experimental model metazoan Caenorhabditis elegans. In addition, transient induction of hsp12 family genes was observed after SMF exposure. The small-heat shock protein gene hsp16 was also induced but to a much lesser extent, and the LacZ-stained population of hsp-16.1::lacZ transgenic worms did not significantly increase after exposure to SMFs with or without a second stressor, mild heat shock. Several genes encoding apoptotic cell-death activators and secreted surface proteins were upregulated after IR, but were not induced by SMFs. Real-time quantitative RT-PCR analyses for 12 of these genes confirmed these expression differences between worms exposed to SMFs and IR. In contrast to IR, exposure to high SMFs did not induce DNA double-strand breaks or germline cell apoptosis during meiosis. These results suggest that the response of C. elegans to high SMFs is unique and capable of adjustment during long exposure, and that this treatment may be less hazardous than other therapeutic tools. Bioelectromagnetics 29:605-614, 2008. (C) 2008 Wiley-Liss, Inc.

Abstract: When the quenching occurs in a superconducting coil, excessive joule heating in normal area may damage the coil. It is necessary to detect quenching in the coil as soon as possible and discharge the magnetic energy stored in the coil. Therefore, we propose a superconducting coil protection system based on an active power method. The system is highly resistant to the noise and does not require cancel voltage taps, so it is useful for both AC and DC coils. We have presented the effectiveness of the system using some test coils cooled in LN2 or LHe. However, we have not discussed the effectiveness of the proposed system for helium-free cryocooled magnets, in which a larger temperature rise occurs after quenching than in liquid-cooled magnets. In this paper, we verify the effectiveness and practicality of the proposed system through coil protection tests for a cryocooled Nb3Al LTS coil. (C) 2008 Elsevier Ltd. All rights reserved.

Abstract: High-field x-ray diffraction and magnetization measurements and differential thermal analysis (DTA) were carried out for polycrystalline MnBi with an NiAs-type hexagonal structure to investigate its magnetic and structural phase transitions. The lattice parameter a rapidly decreases below the spin reorientation temperature T-SR(= 90K) in a zero magnetic field. The parameter c decreases gradually with decreasing temperature and exhibits an anomaly in the vicinity of TSR. By applying a magnetic field of 5 T, the parameter a increases by similar to 0.05% when T < T-SR and varies smoothly when 8 <= T <= 300 K. DTA data show that the magnetic phase transition temperature from the ferromagnetic state to the paramagnetic state increases linearly at a rate of 2KT(-1) with increasing magnetic field up to 14 T.

Abstract: A 30 T superconducting magnet employing Ag/YBa2Cu3O7/Hastelloy (Y123) coated conductors would make precise fundamental research much more accessible. In order to investigate the feasibility of such a magnet, the current stability of the conductor was examined at 30 T for B // c. Liquid helium cooled Y123-coated conductors with copper and silver stabilizing layers were examined for coil quench issues. Instability conditions were studied using a static zero-dimensional model for various copper stabilizing-layer thicknesses. The calculations indicate the existence of a stable sharing current in the copper stabilizer, of about 0.7 A per 1 mu m of copper thickness at 30 Tin liquid helium. This sharing current in the copper stabilizer can be added to the 140% critical current of the Y123 conductor at 30 T for B // c. (C) 2008 The Japan Society of Applied Physics.

Abstract: To carry out long-term experiments requiring a large bore and a constant high magnetic field, a 100 mm bore water-cooled resistive magnet has been designed, which is combined with a cryocooled superconducting outsert as a cryocooled hybrid magnet. The designed double Bitter magnet will produce 10.1 T under a use of 4.5 MW power for a long time operation, and a cryocooled hybrid magnet will be able to keep 18 T in a backup field of 8 T for ten hours economically. Main application of the wide bore cryocooled hybrid magnet is X-ray diffraction measurement under high magnetic fields. The development of a Debye-Scherrer camera system for a 10 T-100 mm bore cryocooled superconducting magnet has started as the first step.

Abstract: The chiral electrode behaviors of magneto-electrodeposited (MED) Ag and Cu films were examined for the electrochemical reactions of D-glucose, L-glucose and L-cysteine. The Ag and Cu films were electrodeposited under a magnetic field of 2 T parallel (+2T) or antiparallel (-2T) to the faradaic current. For MED films of both Ag and Cu, the oxidation current of L-glucose was larger than that of D-glucose on the +2 T-film electrodes, and the results were opposite on the -2T-film electrodes. These facts demonstrate that the MED metal films possess the ability of chiral recognition for D-and L-glucoses. The MED Ag film electrodes also exhibited chiral behavior for the oxidation of L-cysteine.

Abstract: Ambipolar organic field-effect transistors (OFETs) with comparable hole and electron mobilities were fabricated using pentacene single crystals. Ambipolar single-crystal transistors enable us to determine the intrinsic effect of postannealing on the performance of OFETs, which remains controversial. The results confirm that postannealing predominantly causes hole dedoping due to oxygen desorption. (C) 2008 American Institute of Physics.

Abstract: We studied the crystal structure and magnetic properties of the U2Co17-xSix system. The homogeneity range of U2Co17-xSix extends from x = 1.0 to 3.4. The variation of the magnetic properties within the homogeneity range was studied on single-crystalline samples grown by the Czochralski method in a tetra-arc furnace. Results on magnetic anisotropy point to a magnetic state of U up to x = 3.0. (c) 2006 Elsevier B.V. All rights reserved.

Abstract: Field and temperature dependencies of the magnetization measured along the principal axes of a U2Co15Si2 single crystal show that this compound is a ferromagnet with a spontaneous magnetic moment of 14.8 mu(B) per formula unit (at 4.2 K), located in the basal plane of the hexagonal crystal structure. A strong easy-plane magnetic anisotropy (K-1 = -0.97 MJ m(-3) at 4.2 K) is attributed to the U sublattice because Lu2Co15Si2 exhibits easy-axis anisotropy with K-1 = 0.42 MJ m(-3). The easy-plane anisotropy of U2Co15Si2 transforms to a cone of easy axes above 270 K. The magnetization vector approaches the c-axis at 350 K, and the compound has easy c-axis anisotropy up to the Curie temperature T-C = 601 K. (C) 2007 Published by Elsevier B.V.

Abstract: The mechanical properties of Cu and Cu-alloy (Cu-Zr, Cu-Be and Cu-Cr) sheath in situ PIT-processed MgB2 superconducting wires were studied at room temperature (RT) and 4.2 K. The effects of stress/strain on the critical current (I-c) of the wires have also been studied at 4.2 K and in magnetic fields up to 5 T. Alloying the Cu sheath significantly increased the yield stress of the wires. The 0.5% flow stresses of the Cu-alloy sheath wires were 147-237 MPa, whereas that of Cu was 55 MPa. At RT, the serration in the stress-strain curves corresponding to the multiple cracking was observed around a strain of 0.4% and the curve almost saturated beyond that point. The strain dependence of I-c prior to the critical strain (epsilon(irr)) was different depending on the magnetic field; being almost constant at 2 T and increased with strain at 5 T. The Ic decreased beyond epsilon(irr), which was much larger for Cu-alloy sheath wires as compared with Cu sheath wire. The magnitude of epsilon(irr) is due to the difference in the thermal compressive strain in the MgB2 core, which was relaxed by yielding in the sheath materials. The transverse compression tests revealed that the I-c of the Cu-alloy sheath wire did not degrade up to about 95 MPa, which is also higher than that of Cu sheath wire. (c) 2007 Elsevier Ltd. All rights reserved.

Abstract: Magnetization measurements of polycrystalline MnBi were carried out in magnetic fields up to 10 T and in the temperature range from 300 to 773 K, in order to clarify the magnetic properties under high magnetic fields and high temperature. The magnetic phase transition temperature (T-c) at a zero magnetic field is 633 K, which almost linearly increases by 2.3 KT-1 with increasing fields up to 10 T. Furthermore, a metamagnetic transition was observed just above T, indicating that the phase transition is first order. The magnetic entropy change is estimated to be 14 J kg(-1) K-1 for 2 T at T-c using Clausius-Clapayron�s equation, which is almost constant for magnetic fields up to 10 T.

Abstract: The effect of the quality of starting powders on the microstructure and superconducting properties of in situ processed Fe-sheathed MgB2 tapes has been investigated. Three different types of commercial atomized spherical magnesium powder and two different purities of amorphous boron powder were employed. When using the 10 mu m magnesium as precursor powders, the Mg reacted with boron more uniformly and quickly; thus the uniformity of the fabricated MgB2 was improved and the grain size of the MgB2 was decreased. Hence significant critical current density ( Jc) enhancements were achieved for MgB2 tapes. J(c) at 4.2 K for MgB2 tapes made from the 10 mu m Mg and high purity boron powders was at least a factor of ten higher than values measured for MgB2 samples made from all other starting powders. At 20 K, 5 T, the typical J(c) values of the tapes were over 1.0 x 10(4) A cm(-2) and were much better than those of tape samples reported recently.

Abstract: Magnetization and thermoelectric power (Seebeck coefficient) S of the magnetic shape memory compound Ni50Mn36Sn14 were measured in the temperature T range from 4.2 to 330 K under magnetic fields up to 17 T. In 50K < T < 270 K, S has a negative sign, indicating that electron-type carriers dominate in this compound. The anomaly of the S-T curve closely relates to the magnetic and structural phase transition and the negative S value is enhanced by a magnetic field. (C) 2006 Elsevier B. V. All rights reserved.

Abstract: The vortex state in a single crystal of the layered organic superconductor kappa-(BEDT-TTF)(2)Cu(NCS)(2), where BEDT-TTF (or ET) is bis(ethylenedithio)tetrathiafulvalene, was studied by H-1-NMR. Under a low field region around 0.75 T, the vortex-glass-liquid transition was demonstrated by a diverging of the longitudinal nuclear spin relaxation rate and peak broadening in spectra. Under a high field region near the upper critical field H-c2(0)similar or equal to 7 T, the curvature of nuclear spin relaxation curves showed a drastic change at the temperature where the emergence of the quantum vortex slush state was reported. The mechanism in this curvature change was discussed in terms of the fluctuating field produced by fragments of vortex glass.

Abstract: Relaxation of the thermal residual strain in Nb3Sn wires is realized through cycles of multiple torsion loadings (�pre-torsion�) at room temperature. As a consequence, the critical current, I-c, is enhanced. This effect is stronger than previously reported mechanical treatments of multiple bending (�pre-bending�). The maximum I-c is attained for complex mechanical treatments of pre-torsion and pre-bending. Complex treatments allow efficient and relatively independent control of residual strain relaxation over all three directions of the wire, resulting in enhancement of I-c towards the theoretical limit of the material. Our findings have an immediate positive impact on the performance of Nb3Sn wires and, hence, on their applications (e.g. react-and-wind coils).

Abstract: We have performed powder X-ray-diffraction measurements on MnFeP0.46As0.54 in fields up to 5T in the temperature range 8-310K. The compound which has the hexagonal Fe2P type of structure shows a field-induced isostructural phase transition. We found that the cell volume decreases slightly and continuously with increasing magnetic field, although the lattice parameter ratio c/a drastically changes. A tentative analysis of the dependence of the lattice parameters on the magnetization has been carried out using the extended Bean-Rodbell model. (c) 2006 Published by Elsevier B.V.

Abstract: As-grown MgB2 thin films were prepared by a MBE method under the conditions of low temperature, low deposition rate and high vacuum for applications in electric devices. The MgB2 thin films deposited on MgO and Ti buffered ZnO substrates have considerably higher J(c) under magnetic fields among MgB2 thin films reported before. The value of Jc for the MgB2 thin film deposited on Ti buffered ZnO has been 5.8 x 10(5) A cm(-2) at 10 K, 5 T in the magnetic field applied parallel to the c axis. In the angular dependence of J(c), the peak of J(c) attributable to c-axis-correlated pinning centres has been observed when the magnetic field was applied parallel to the c axis.

Abstract: Transport current properties of the steady and unsteady operating modes and thermal runaway conditions of the Ag-sheathed Bi2Sr2CaCu2O8 composite superconductors are theoretically studied in DC magnetic fields. It is shown that the temperature of a composite is not equal to the coolant temperature before thermal runaway. As a result, the shape of the voltage-current characteristics of high-T-c superconducting composites has only a positive slope during continuous current charging both before and after thermal runaway. That is why the voltage-current characteristics of high-T-c superconductors do not define the boundary of the thermal runaway. This peculiarity has to be considered during experiments at which the critical or quench currents are defined.

Abstract: Chiral polyaniline electrodes were prepared by the magneto-electropolymerization (MEP) method. Cyclic voltammograms (CVs) of L-ascorbic acid (L-AA), D-isoascorbic acid (D-AA), and L-3-(3,4-dihydroxyphenyl) alanine were measured on the MEP polyaniline electrodes and their electrode reactions were electrocatalytic. The CV peak currents varied depending on the chirality of the polyaniline and the optically active species, while the peak potentials were independent of the chirality. The CVs of L-AA and D-AA were also measured on a Pt electrode in a (-)- camphor-10-sulfonic acid supporting electrolyte solution, and the chiral behavior was observed in the peak potentials. It is considered that the electrocatalytic process is responsible for the chiral electrochemical behavior on the polyaniline electrodes.

Abstract: UGe2 is a ferromagnetic heavy-fermion (HF) superconductor, which provides superconductivity under pressure in the range of 1.0 to 1.5 GPa. In this paper, we conducted detailed magnetization experiments up to 27 T and at atmospheric pressure. Magnetization along the a-axis indicates typical ferromagnetic property. On the other hand, magnetization along the b-axis is quite a bit smaller than that of the easy a-axis. The magnetocrystalline anisotropy constant is the same as the rare earth ferromagnet Nd2Fe17, which indicates that UGe2 is a highly anisotropic ferromagnet.

Abstract: Fe-sheathed MgB2 tapes with cheap stearic acid, Mg stearate and Zn stearate doping were prepared through the in situ powder-in-tube method. It is found that J(c), H-irr and H-c2 were significantly enhanced by doping. Compared to the pure tapes, J(c) for all the doped samples was improved by more than an order of magnitude in a high-field regime. At 4.2 K, the transport J(c) reached 2.02 x 10(4) A cm(-2) at 10 T for the Zn stearate doped tapes and 3.72 x 10(3) A cm(-2) at 14 T for the stearic acid doped samples, respectively. Moreover, at 20 K, H-irr for the Zn stearate doped tape achieved 10 T, which is comparable to that of the commercial NbTi at 4.2 K. The improvement of J(c)-H properties in doped samples can be attributed to the increase of H-c2 resulting from the incorporation of C atoms into the MgB2 crystal lattice as well as a high density of flux-pinning centres.

Abstract: In order to obtain the information about magnetic states of reentrant ferromagnet, SmMn2Ge2, we have studied the pressure effect on magnetocaloric properties by magnetization measurements under high pressures up to 1.2 GPa in the temperature range from 5 to 300 K. Using the Maxwell relation, we estimated the magnetic entropy change vertical bar Delta S-M vertical bar to be 0.65 JK(-1) mol(-1) at T-1 (= 100K) and 0.53 JK(-1) mol(-1) at T-2 (= 150K) under 0.1 MPa. By applying pressures up to 0.5GPa, vertical bar Delta S-M(T-1)vertical bar is enhanced (2.0 JK(-1) mol(-1)), while vertical bar Delta S-M(T-2)vertical bar is slightly suppressed (0.4 JK(-1) mol(-1)). The obtained values of vertical bar Delta S-M vertical bar were discussed on the basis of a mean field theory using a two-sublattice model.

Abstract:

Abstract: Critical temperature T-c of the Li-2(Pd1-xPtx)(3) B was reported to be 7-8 K for x = 0 and 2.2-2.8 K for x = 1. In this article we present our preliminary results on behavior of magnetization-temperature curves with starting composition of Pd-B precursor, y-Li concentration in LiyPd3B and post-annealing of the Pd-end compound. Results suggest that to maximize T-c ratio Pd: B should be close to 3: 1, while y-Li has to be optimum. The lowest T-c for LiyPd3B was 4.4-4.6 K, while post-annealings at 560 degrees C allowed enhancement of T-c up to 8.2-8.4 K. Compositions Li(2)Z(3)B with Z = Ni, Ru, Rh, Re, Ag are not superconducting down to 1.8 K. Exception is composition with Re showing superconductivity due to Re3B compound. All samples were prepared by arc melting. (c) 2007 Elsevier B.V. All rights reserved.

Abstract: The effect of Zr and Zn doping on superconducting properties and microstructures of filamentary Eu-Ba-Cu-O superconductors prepared by a solution spinning method has been investigated. Samples doped with small amounts of Zr and Zn showed relatively high J(c) values of around 2 x 104 A cm(-2) at 77 K and 0 T-c which was two times larger than that of the pure Eu 123 filament. The temperature range for the partial melting in reduced oxygen partial pressure obtained the J(c) value higher than 104 A cm(-2) at 77 K became wider when Zr and Zn were added. From the SEM observation, a small amount of Zr and Zn doping was found to be useful to reduce the size of Eu211 particles, whereas it showed adverse effects on the dispersion of Eu211 particles and compositional homogeneity in a Eu123 matrix. In the case of Zn doping, although sample showed high J(c) value larger than 104 A cm(-2) at magnetic field lower than 2 T-c a J(c) value monotonically decreased at above 3 T and superconductivity was disappeared at 11 T. On the contrary, in spite of the fact that a J(c) value of sample with 0.5 at.% Zr decreased by applying only a magnetic field of 0.2 T-c superconductivity could be maintained up to 17 T at 77 K. (C) 2007 Elsevier B.V. All rights reserved.

Abstract: We have studied SmBa2Cu3Oy (Sm123) thin films fabricated by low temperature growth (LTG) technique. The critical current den. particles (NLP) were comparable to that of sities (J(c)s) in magnetic fields at 77 K of the LTG-Sm123 film embedded nanosized low-T. NbTi wire at 4.2 K. Furthermore, at low temperatures of 65 and 40 K, the J(c)-B curves of the LTG-Sm123 film were superior to even that of Nb3Sn wire at 4.2 K and the anomalous peaks were observed on the J(c)-B and F-p-B curves. Based on the scaling of the flux pinning force, we found that fluxes in the film would be pinned at grain boundary mainly and the anomalous peaks were caused by the NLP. (C) 2007 Elsevier B.V. All rights reserved.

Abstract: Carbon nanotube-doped Fe-sheathed MgB2 wires and tapes with different doping levels were fabricated by the in situ powder-in-tube method. The phases, microstructures and flux pinning were characterized by XRD, SEM/TEM, magnetic and transport-property measurements. It is found that carbon nanotubes (CNTs) doping resulted in a significant enhancement in the field dependence of critical current density J(c) for all the added wires and tapes. The J(c) in 13 T and 4.2 K for the CNTs doped tapes (optimal MgB1.9C0.1) increased by a factor of 11 compared to that of the undoped sample. The observed J(c)(B) improvement in the added samples is attributable to the enhanced flux pinning caused by the CNTs doping. (c) 2007 Elsevier B.V. All rights reserved.

Abstract: High performance Fe-cladded MgB2 taps were prepared by the in situ powder-in-tube method utilizing very cheap stearic acid (C18H36O2) as dopants. The amount of stearic acid was varied from 0 to 30 wt%. We found that a significant enhancement of J(c), H-irr, and H-c2 in comparison with undoped samples was easily achieved. At 4.2 K, the transport J(c), for the best doped tapes (10 wt%) reached 2 x 10(4) A/cm(2) at 10 T and 3.7 x 10(3) A/cm(2) at 14 T, respectively, an order of magnitude higher than for the pure tapes. In particular, at 20 K, the irreversibility field of the 10 wt% doped tape was around 10 T, which is comparable to the upper critical field of the commercial NbTi at 4.2 K. The results demonstrate great potential of MgB2 tapes for superconducting magnets.

Abstract: Appling the in situ powder-in-tube method, 11 meter long Fe-sheath MgB2 superconducting wires with outer diameter 1.75 mul were fabricated, using 99.5% Mg powder and 99.9% amorphous boron powder doped with 30 nm SiC powder as starting materials. This procedure begins with ball-milling of the mixture powder immersed in acetone solution in a jar and subsequently drying in vacuum. Then the iron tube loaded with the powder mixture was grooved, swaged and drawn to the final wire size. The transition temperature, microstructure, lattice constant and chemical element distribution were evaluated by SQUID, XRD, SEM and EDS, respectively. It was found that T-c(onset) and Delta T-c are 35. 1 K and 5.3 K, respectively. All samples containing a small amount of MgO, exhibit rather uniform microstructure. Besides, by nano-SiC doping, the MgB2 lattice distortion due to substitution of boron by carbon, results in forming effective flux pining centers, which significantly improves the critical current, and the C element was uniformly distributed in the MgB2 matrix. The standard four-probe measurement shows that all the 10 sample points, which were evenly cut at 1 meter intervals of the 11 meter length wire, have good superconducting homogeneity with critical current values fluctuating within 10% under the applied fields vavying from 10 to 18 Tesla, and all J(c) values are above 10(4) A/Cm-2, with the highest value reaching 1.2 x 10(4) A/cm(2) at 4.2 K and 10T.

Abstract: The transport critical current density J(c) is one of the most important properties for practical applications of high-T-c superconductors. The J(c) properties of high-T-c superconductors are highly dependent on the microstructural texturing of the superconducting phase. In order to improve the grain alignment of the superconducting phase melt-processing in high magnetic fields is a very effective method based on the anisotropy of magnetic susceptibility. For Bi-based superconducting bulks and tapes, there have been many studies using the in-field melt-processing and large J(c) enhancements due to the texture improvement are observed. In this study, we employed melt-processing in high magnetic fields for the Ag/Bi2212 round wires, which are much superior to thin tapes in fabricating superconducting magnets. Since the J(c) properties of Ag/Bi2212 are very sensitive to the maximum temperature of the heat treatment, we performed the melt-processing under various maximum processing temperatures. During the heat treatment, a magnetic field of 0 T or 5 T was applied using a cryocooled superconducting magnet. For the wires heat-treated under a magnetic field, small increase of the J(c) values were observed. From the results of the detailed analysis of the E - J properties, we found that there are possible microstructural changes due to the in-field process. It is suggested that the in-field heat-treatment is very effective for not only J(c) enhancement but also the n-value improvement for Bi2212 conductors.

Abstract: Magnetization measurements and differential thermal analysis (DTA) of polycrystalline MnBi were carried out in magnetic fields up to 14 T and in 300-773 K, in order to investigate the magnetic phase transition. The magnetic phase transition temperature (T,) at a zero magnetic field is 628 K and linearly increases with increasing fields up to 14 T at the rate of 2 KT-1. A metamagnetic transition between the paramagnetic and field-induced ferromagnetic states was observed just above T-t. The exothermic and endothermic peaks were detected in the magnetic field dependence of DTA signals in 626-623 K, which relates to the metamagnetic transition. The obtained results were discussed on the basis of a mean field theory.

Abstract: (Nd0.33SM0.33Gd0.33)(1.18)Ba2.12Cu3.09Oy, filaments have been successfully fabricated by a solution spinning method and OCMG processing. We have systematically investigated the relationship between cooling rate from the partial-melting temperature and transport J(c) value for filamentary samples treated in 0. 1%O-2 + Ar. It was found that both the Jc value and the microstructure of samples depended on the cooling rate. The samples partially melted at 1050 degrees C and cooling rate of 10-50 degrees C/h showed J(c) value higher than 104 A/cm(2). The maximum J(c) value of 3.0 x 10(4) A/cm(2) was obtained for 40 degrees C/h sample. The transport J(c) was also measured at 83-90 K in external magnetic fields up to 17 T. The 10 degrees C/h sample exhibited superior J(c) behavior and a J(c) value of 1.1 x 10(3) A/cm(2) at 83 K was maintained up to 17 T, in which fine (Nd,Sm,Gd)(2)BaCuO5 particles about I pm in diameter were homogeneously dispersed. (C) 2007 Elsevier B.V. All rights reserved.

Abstract: Two practical Nb3Sn composite wires (short samples) were investigated from the points of view of critical current, I-c, and cracks evolution versus number of bending load cycles. Bending was applied manually at room temperature using a block-form with curved surface corresponding to applied bending strains of 0.5% and 0.8%. It was applied in plane, alternatively in one direction and in the opposite one up to 130 times. We shall use for this mechanical treatment term pre-bending. The wires had approximately the same diameter but a different architecture: one was of conventional type (standard US-Japan wire, Hitachi Cable) and the second one was CuNb reinforced wire (Furukawa Electric Co. Ltd.) with reinforcement located near-the-edge. It was found that critical current maximizes gradually with the number of bendings and the maximum value of I-c, is attained for a number of bending loadings, N-pb, of about 15. Beyond this optimum N-pb, critical current is constant. Optimum N-pb is likely not dependent on the wire, applied field or pre-bending strains. Results suggest that Cu is important in the work hardening process. Work hardening during pre-bending is imposing limitations in application of this technically convenient mechanical treatment for release of the residual strain and further enhancement of I-c. Semi-quantitative analysis of the electron microscopy observations shows that for our experimental conditions the density of cracks is approximately constant being in agreement with described I-c, behavior. Other possible consequences of our results are discussed. Among the most interesting issues is possibility of the 3D independent control of yielding and hence of residual strain release. Several new practical ideas that will need future confirmation are proposed: e.g. application of loading-unloading cycles of torsion treatment in combination with tensile or pre-bending treatments might be useful.

Abstract: As-grown MgB2 thin films on Si substrates with high J(c) under magnetic fields were prepared by electron-beam evaporation. The value of J(c) has been enhanced by the deposition of MgB2 thin film in an O-2 atmosphere. The MgB2 thin film deposited in the O-2 atmosphere (O-2-doped film) has exhibited considerably higher J(c) in magnetic fields among MgB2 thin films reported before. It has been found that the high J(c) of the O-2-doped film is attributable to the flux pinning with grain boundaries strengthened by an introduction of MgO along grain boundaries. In a high magnetic field, a peculiar behavior of E-J characteristics where E-J curves vary in two stages was observed. This behavior also originates from the flux pinning with strengthened grain boundaries.

Abstract: Nano-C doped Fe-sheathed MgB2 tapes with different doping levels were fabricated using a powder-in-tube method and an in situ reaction. The effects of nano-C doping on the transition critical temperature, microstructure, critical current density, and flux pinning of MgB2 tapes were studied. Compared to the undoped tapes, critical current density J(c) for all the C-doped samples with different doping level was enhanced by more than an order of magnitude in magnetic fields above 10 T. This result indicates that flux pinning was effectively enhanced by the nano-C doping. Highly dispersed nanoparticles; and the substitutions of B by C are proposed to be responsible for the improvement of J(c) -B properties.

Abstract: MgB2 tapes with 5 at.% Bi addition were fabricated through the in situ powder-in-tube method. Heat treatment was carried out at 700 degrees C and 800 degrees C for 1 h. The phase, microstructure, superconductivity and flux pinning ability were characterized, by XRD, SEM, magnetic and transport measurements. The critical current density J(c) and J(c)-B performance for the doped and undoped samples are also given. It is found that nano-Bi doping decreased the magnetic field sensitivity of J(c), indicating an improvement of flux pinning. At 4.2-K, 10 T, J(c) values of the Bi doped tapes enhanced about 2.5 times compared to that of undoped samples. The mechanism for improved J(c)-B performance of Bi-doped MgB2 tapes is investigated.

Abstract: An application of the prebending effect to a cabling process using Nb3Sn strands was demonstrated. The prebending effect is the enhancement effect of superconducting properties due to the repeated prebending treatment for practical bronze-route Nb3Sn wires. CuNb/Nb3Sn and Cu/Nb3Sn strands were applied prebending treatment using 10 fixed pulleys with 0.8% prebending strain. Four kinds of triplets, i.e., prebent CuNb/Nb3Sn, no-prebent CuNb/Nb3Sn, prebent Cu/Nb3Sn and no-prebent Cu/Nb3Sn triplets were fabricated. Critical currents were measured for the four kinds of triplets in magnetic fields up to 11 T at 4.2 K. The obvious critical current enhancement due to the prebending effect was maintained for the prebent CuNb/Nb3Sn triplet. The results imply that the prebending treatment for high-strength Nb3Sn strands is applicable to the cable conductor fabrication.

Abstract: Magnetic field dependencies of the I-c of the IBAD/CVD-YBCO short tape sample and its small coil sample were measured in high fields, up to 18 T at 77 K. Compared with the I-c of the tape sample, the I-c of the coil sample at 0.1 mu V/cm showed the same tendency in high fields. If YBCO tape is applied to a high-field coil application, the application should be operated at a temperature which is lower than 77 K. Using long CVD-YBCO tape, six stacked pancake coils were fabricated. Various current tests were conducted using one of these stacked coils. In AC current tests, thermal stability of the YBCO coil was estimated. When the peak values of AC current were 1.2 times higher than the maximum DC current in a thermal stable state, I-dcmax, and the average electric field of the coil at the first triangular wave was about 10 times higher than 1 mu V/cm criterion, the peak values of the built-up voltage did not tend to increase even after the 99th triangular wave current, and thermal run-away in the coil was not observed. In DC current with overlapped pulse current tests, the maximum peak current of the coil in a thermal stable state was obtained as a function of DC current and sweep time. It was 1.3 times higher than I-c and 1.4 times higher than I-dcmax in a test condition. These results indicate that the YBCO coil has high potential in short-time, over-current operations at high temperatures. In cases where built-up voltages did not disappear, they began to increase just after the coil currents reverted to the initial DC currents. It was found that DC current influenced the increasing speed of built-up voltages once the pulse current had decreased to zero.

Abstract:

Abstract: The microstructure and superconducting properties of Bi-2223 superconductor fabricated in high magnetic fields were investigated. The results shows that the Bi-2212 grains with their c-axis parallel to the magnetic field were formed after the partial-melting and solidification in 8 T magnetic field, and transformed into the Bi-2223 grains with c-axis alignment during the further sintering process at 840 degrees C without magnetic field. The conversion of Bi-2212 grains to Bi-2223 grains has the heredity in grain alignment. The mixed structures of the Bi-2223 and the Bi-2212 grains with their c-axis parallel to the magnetic field are formed in samples sintered at 850-855 degrees C in 10 T magnetic field. When sintered in 10 T below 845 degrees C, a high proportion of Bi-2223 phase is obtained, however no preferred orientation is observed. The Bi-2223 grains with their c-axis parallel to the axial direction of the vertical tube furnace are formed not only on the surface, but also in the center of the sample sintered at 850 V for 120 h in a 15 degrees C/cm temperature gradient without magnetic field. Moreover, the samples sintered in the temperature gradient and in a 10 T magnetic field have a stronger c-axis alignment of Bi-2223 phase.

Abstract: Precise magnetization measurements have been made on the weak itinerant electron ferromagnet CoVSb. The magnetic moment at 4.2 K and the Curie temperature T-C are 0.16 mu B/f.u. and 45 K, respectively. Below 10 K, the decrease in the square of the spontaneous magnetization M-s(T)(2) is proportional to T-2. However, over a wide temperature range from 24 K to the Curie temperature, the decrease in M-s(T)(2) is proportional to T-4/3. The results obtained are analyzed using spin fluctuation theory.

Abstract: The structure and magnetocaloric properties of the Fe-doped HoTiGe compound were investigated by means of scanning electron microscopy (SEM), energy dispersive spectroscopy, x-ray diffraction, magnetometry, and calorimetry. As with the early studies on the undoped compound, the Fe-containing alloy exhibited an antiferromagnetic-to-paramagnetic transition and a magnetocaloric effect peak at 90 K. The magnetization (M) versus temperature (T) data showed peaks at 10 and 90 K, while M versus field (H) curves showed the presence of a field-induced transition for all T < 120 K; additionally, for all T < 60 K, open hysteresis loops at the magnetic transitions were observed. XRD measurements between 10 and 60 K under various magnetic fields up to 3184 kA/m (40 kOe) showed that the hysteresis was not accompanied by any change in crystallography. The magnetization derived entropy change -Delta S-m vs T plot also showed the presence of two peaks, at 20 and 90 K; but below 15 K, -Delta S-m increased steeply with decreasing temperature. It is believed that the minor phases in the Fe-doped alloy give rise to the magnetization-derived -Delta S-m peak at 20 K. The heat-capacity-derived -Delta S-m vs T plot for the Fe-doped alloy also showed the presence of two peaks at 20 and 90 K. However, the heat-capacity-derived -Delta S-m did not show a rapid rise with decreasing temperature below 15 K. (C) 2006 American Institute of Physics.

Abstract: The operating thermal and electric modes of a high-T-c superconducting composite in partially and fully penetrated states induced by the charging current are investigated. They were studied under conditions in which the current charging rate, the volume fraction of the superconductor in a composite or the temperature of the cooling bath were changed. The transient behaviour of the voltage - current dependence, which is characteristic during stable and unstable increases in electric field inside the composite under a continuous current charging, is discussed. Simulations were done using zero- and one-dimensional steady and unsteady thermoelectric models with a power equation describing the virgin voltage - current characteristic of a superconductor. It is found that some thermoelectric trends underlie the shape of the voltage - current characteristic of the high-T-c superconducting composite. These have to be considered during experiments in which the critical or quench currents are defined. First, in the initial stage of the fully penetrated regime ( in the low voltage range), the electric field distribution does not have a uniform character. These states depend on the volume fraction of the superconductor and the current charging rate: the higher these quantities, the higher the heterogeneity of the electric field. Second, during the stable over-critical regime ( in the high voltage range) occurring in complete penetration modes, the evolution of the electric field may depend on the relevant temperature increase of a composite according to the corresponding increase in its temperature-dependent heat capacity. Consequently, the shape of the voltage - current characteristic of a composite high-T-c superconductor during continuous current charging, both before and after thermal runaway, has only a positive slope. Moreover, it is proved that the growth of the fully penetrated part of the voltage - current characteristic becomes less intensive when the current charging rate or the coolant temperature increase. That is why the voltage - current characteristic of a high-T-c superconductor cannot determine the boundary of onset of thermal runaway. It is also confirmed that there is a thermal degradation mechanism of the current-carrying capacity of the composite. In particular, according to this mechanism, the quench currents do not increase proportionally to an increase in the amount of superconductor in a composite.

Abstract: The strength of single- and polycrystalline ZnSe was investigated at elevated temperatures by means of compressive deformation. The yield stress of ZnSe was rather low around 13MPa, easily deformed even at low temperatures 150 degrees C. The activation energy for dislocation motion in ZnSe was estimated to be 0.5-0.7eV. The intrinsic stacking fault energy was measured 7-9 mJ/m(2) from the dissociation width similar to 20nm of dislocations into partials by weak-beam transmission electron microscopy. The recombination-enhanced dislocation motion was detected through the change of dislocation morphologies induced by the electron irradiation during weak-beam observation.(c) 2006 Elsevier B.V. All rights reserved.

Abstract: MoSi2-doped MgB2 tapes with different doping levels were prepared through the in situ powder-in-tube method using Fe as the sheath material. The effect of MoSi2 doping on the MgB2/Fe tapes was investigated. It was found that the highest J(C) value was achieved in the 2.5 at.%-doped samples, more than a factor of 4 higher than the undoped tapes at 4.2 K, 10 T, then further increasing the doping ratio caused a reduction of J(C). Moreover, all doped tapes exhibited improved magnetic field dependence of J(C). The mechanism of J(C) enhancement by MoSi2 doping is also discussed.

Abstract: The thermal runaway conditions of the composite Bi2Sr2CaCu2O8 superconductor cooled by liquid helium or liquid hydrogen are compared. The study based on the static analysis of thermoelectric modes was made when the volume fraction of the superconductor in a composite was varied. Some specific trends underlying the onset of thermal runaway in superconducting composites cooled by liquid coolants are discussed. It is stated that the operating modes of superconducting composites may be characterized by stable states during which the current-carrying capacity of a superconductor is not effectively used even with a high amount of superconductor in the composite. These states are possible due to the corresponding temperature variation of the resistivities of the matrix and the superconductor in the high operating temperature range. They have to be considered in experiments when the critical current of a superconductor is determined or when the optimal stable operating modes of the current-carrying elements based on the Bi2Sr2CaCu2O8 superconductor, which is cooled by liquid coolant, are defined.

Abstract: We investigated the effect of ZrSi2 and SiC doping on the microstructure, critical current density J(c) and flux pinning of Fe-sheathed MgB2 tapes prepared by the in situ powder-in-tube method. Heat treatment was performed at a low temperature of 650 degrees C for 1 h. The phases, microstructure and flux pinning were characterized by means of x-ray diffraction, scanning electron microscope, magnetic and transport property measurements. It was found that the tapes doped with nanoscale SiC had the best pinning performance, while the ZrSi2 powder showed a similar improved field dependence of J(c) compared with undoped samples. J(c) values for the SiC doped samples were enhanced by two orders of magnitude at 4.2 K in magnetic fields above 8 T. At 4.2 K and 10 T, the J(c) reached similar to 1.5 x 10(4) A cm(-2). Moreover, the critical temperature for the doped tapes decreased slightly ( < 1.2 K). Microstructural analysis shows that very good grain connections or/and grain refinement were obtained for the doped tapes. The mechanism of the enhancement of the flux pinning is also discussed.

Abstract: Thin films of MgB2 on r-cut Al2O3 substrates have been grown by pulsed-laser deposition (PLD) using a Nd-YAG laser (fourth harmonic-266 nm) instead of the popular KrF excimer laser. The growth window to obtain superconducting films is laser energy 350-450 mJ and vacuum pressure with Ar-buffer gas of 1-8/10 Pa (initial background vacuum 0.5-1 x 10(-3) Pa). Films were deposited at room temperature and post-annealed in situ and ex situ at temperatures of 500-780 degrees C and up to 1 h. Films are randomly oriented with maximum critical temperature (offset of resistive transition) of 27 K. SEM/TEM/EDS investigations show that they are mainly composed of small sphere-like particles (<= 20 nm), and contain oxygen and some carbon, uniformly distributed in the flat matrix, but the amount of Mg and/or oxygen is higher in the aggregates-droplets (100-1000 nm) observed on the Surface of the film�s matrix. Some aspects of the processing control and dependences on film characteristics are discussed. The technique is promising for future development of coated conductors.

Abstract: Fe-sheathed MgB2 tapes were prepared by the in situ powder-in-tube technique using nanometre Si/N/C, SiC whiskers and SiC as doping materials, respectively. The doping effect on phase composition, microstructure and critical current properties was investigated. Heat treatment was performed at 650 degrees C for 1 h under an argon gas atmosphere. All the doped tapes were found to have significantly enhanced critical current density J(C) at 4.2 K in magnetic fields up to 14 T compared with their undoped counterparts. Moreover, the tapes doped with nano-SiC had the best pinning performance, while the SiC whiskers and Si/N/C powders showed a similar improved field dependence of J(C) compared to undoped samples. At 4.2 K and 10 T, J(C) for the nano-SiC doped samples increased by a factor of 32. Even for Si/N/C doped tapes, a 16-fold improvement in the magnetic field J(C) was observed. It is inferred that the different chemical properties of the Si and C elements in SiC, SiC whiskers and Si/N/C led to the J(C)-B difference.

Abstract: Applicability of beta-ray-induced X-ray spectrometry (BIXS) for in situ measurements of tritium retention by plasma-facing materials in ITER was examined using two gamma-emitters and a divertor tile with metallic supports employed during D-T fusion experiments in JET Measurements of the tile with a gamma-emitter showed that the presence of the gamma-field has no influence in the shape of the beta-ray-induced X-ray spectra, although the whole intensity in the observed energy region was dependent on radioactivity of the gamma-emitters. To simulate more accurately the in-vessel environment of PFMs, one of the divertor tiles with metallic supports was subjected to BIXS measurements. Although the metallic supports were gamma active, no significant effect was observed on the recorded X-ray spectrum. These results clearly indicate that BIXS can be applied to in situ measurements of tritium retention by PFMs with a simple shielding of the X-ray detector. (c) 2005 Elsevier B.V. All rights reserved.

Abstract: We have studied the magnetic properties of Ce(Fe1 xCox)(2) with x = 0 and 0.05 by magnetization measurements under high pressure. In both compound, the remarkable suppression of the magnetization is observed below T* in the ferromagnetic (FM) state under 1.2 GPa. T* shifts to lower temperature with increasing the magnetic field, and the extrapolated value to the zero magnetic field is estimated to be 95 and 123 K. These high pressure and magnetic field effects are probably due to the enhancement and the suppression of the AFM spin fluctuation, respectively. (c) 2005 Elsevier B.V. All rights reserved.

Abstract: The structural and magnetic properties of the ferromagnetic Heusler alloy Ni50Mn36Sn14 were studied by magnetization and x-ray powder diffraction measurements in fields up to 5 T. The alloy undergoes the martensitic transformation from the L2(1)-type cubic structure with the lattice parameter a(c)=0.5988 nm into an orthorhombic structure with the lattice parameters a(o)=0.8617 nm, b(o)=0.5702 nm and c(o)=0.4359 nm at M-s=220 K with a thermal hysteresis of 40 K. The cell volume contracts by 0.37% and the magnetic moment decreases by 50% at M-s. Furthermore, we directly observed the field-induced reverse martensitic transformation. (c) 2006 American Institute of Physics.

Abstract: We have performed detailed magnetization, specific heat and powder X-ray diffraction measurements under magnetic fields, for obtaining information on the magnetic and the structural properties of re-entrant ferromagnet SmMn2Ge2 with the ThCr2Si2-type tetragonal structure. The lattice parameter a decreases by about 0.1%, while the parameter c increases slightly by about 0.02% in the antiferromagnetic (AFM) state, compared with the ferromagnetic (FM) and re-entrant ferromagnetic (RFM) states. In the AFM state, the structural distortion recovers by applying a magnetic field, accompanied with the metamagnetic transition from the AFM to the forced FM states. The results of a magnetocaloric effect indicate that the magnetic entropy change at these phase transitions is mainly due to the change of the Sm magnetic state. (c) 2005 Elsevier B.V. All rights reserved.

Abstract: The systematics of the bandwidth- and filling-controlled metal-insulator transitions (MITs) have been investigated for R2Mo2O7 family (R=Nd, Sm, Eu, Gd, Dy, and Ho) by infrared spectroscopy. The substantial role of electron correlation in driving the MIT is verified. With changing the R ionic radius (r) or equivalently the one-electron bandwidth (W), the MIT occurs in a continuous manner at r(c)approximate to r(R=Gd). The T=0 K gap continuously vanishes as Delta proportional to(r(c)-r), while at the metallic side the linear decrease of Drude weight is followed toward r(c). In the metallic compounds, some of the infrared-active phonon modes show remarkably large Fano asymmetry correlating with the Drude weight. These Mo-O-Mo bending modes strongly couple to the conduction electrons via effective modulation of the bandwidth. Even for r less than or similar to r(c) a minimal level of hole doping closes the correlation gap, for example, the barely insulating Gd2Mo2O7 is turned to an incoherent metal by 5% partial substitution of Gd3+ with Ca2+. However, even on further doping no coherent electronic states are formed, indicating the role of the disorder-induced localization effect besides the dominant correlation effects.

Abstract: In this paper, we review our recent results on magnetic refrigerants MnAs1-xSbx and MnFeAs0.5P0.5 by powder X-ray diffraction measurements in fields up to 5 T and in the temperature range from 8 to 320 K. MnAs shows a first-ordered structural transition with the volume expansion of 2.1% accompanied by a metamagnetic transition, but MnAs0.9Sb0.1 exhibits an isostructural transition with the volume expansion of 1.1%. The cell volume of MnFeAs0.5P0.5 slightly (-0.4%) and continuously decreases with increasing a magnetic field through the metamagnetic transition.

Abstract: The effect of transverse geometries of the slab of composite high-T-c superconductors on their stable and unstable thermal and electrodynamics transient states in the incomplete and complete penetration modes during the current charging are discussed. The transient period when the electric field that is induced by the charged current becomes more homogeneous during the initial stage of the complete penetration mode in the sub-critical voltage range is studied. In the over-critical voltage range, the cross-section shape of the slab affects its stable and unstable temperature variation. As a result, the current instability condition is not identical for high-T-c superconducting composite tapes that have the same cross-sectional area with various shapes of the cross-section. The condition depends on their thickness: the less thickness, the more stable the current distribution in the composite superconductors with the same cross-sectional area. This feature is a result of the unavoidable reduction of the current-carrying capacity of a high-T-c superconducting composite by the temperature increase. This reduction is caused by the relevant temperature dependence of electrodynamics states of the composite. This temperature dependence happens even during a stable stage of the current charging. These mechanisms must be considered during experiments at which the critical or quenching currents are defined. (c) 2006 Elsevier B.V. All rights reserved.

Abstract: We have successfully developed a cryocooled superconducting magnet which generates the world�s highest magnetic field of 18.1 T. This conduction-cooled superconducting magnet has a 52-mm room temperature bore. The magnet consists of three sections; a high-T-c superconducting insert coil, four Nb3Sn coils, and an outer NbTi coil. Each section was energized by an individual power supply. The superconducting coils are cooled conductively by a Gifford-McMahon-Joule-Thomson (GM-JT) cryocooler with a cooling capacity of 4.3 W at 4.3 K. The ramp-up time to 18 T is 60 min. The high-T-c insert coil is composed of 25 double- pancake coils using Ag/(Bi,Pb)(2)Sr2Ca2Cu3O10 (Bi2223) high-T-c superconducting tape with stainless steel tape reinforcement. The reinforcement co-winding reduces the effective hoop stress down to 48 MPa, and, hence, Bi2223 tape can be used. The innermost of the Nb3Sn section is made of an internal-tin-processed Nb3Sn wire because this wire can withstand high critical current density in high magnetic fields. Other three coils require high mechanical strength. They experience hoop stress of 230 MPa, and in this case, bronze-processed high-strength Nb3Sn wires were used. The magnet has a distinctive feature, that is the high-T, insert coil is replaceable. It indicates that the magnet can be used as a 15.5 T back-up magnet for a new insert coil. A Y123 coil is a candidate for the replacement. (c) 2006 Elsevier B.V. All rights reserved.

Abstract: Substitution of Y for U in the itinerant 5f-electron metamagnet, UCoAl, transforms the system to a ferromagnetic state. Application of external hydrostatic pressure above 0.3 GPa suppresses the spontaneous ferromagnetism and restores the paramagnetism with field-induced transition to ferromagnetic state. However, the transition becomes of the second order instead of the first-order one in parent UCoAl.

Abstract: The magnetic levitation for diamagnetic materials provides a quasi-microgravity condition and enables containerless melting for materials synthesis. Laser furnaces have been developed and containerless melting experiments under the magnetic levitation condition were performed so far. In order to perform a homogeneous heating of a levitating sample, which was difficult in laser furnaces, a new magnetic levitation furnace has been developed using an electric furnace. Spherical samples of a cycloolefin polymer were obtained by using this furnace under the magnetic levitation condition. (c) 2006 NIMS and Elsevier Ltd. All rights reserved.

Abstract: E - J properties of the high-T, materials are related to the distribution of the local critical current density J(c). From the previous results on Bi2212 thick films and practical Ag-sheathed Bi2212 tapes, we found that the distribution of the local J. is much affected by microstructures, and the local J(c) distribution becomes broad and asymmetric for well aligned plate-like Bi2212 grains. However, from a viewpoint of microstructures, the origin of the asymmetric J(c) distribution remains unclear. In order to understand the relationship between the J(c) distribution of Bi2212 materials and microstructure, we propose a �two directional J(c) distribution model�. In this model, the difference of the local J(c) distributions for various kinds of Bi2212 samples was explained in terms of the two different directional current flows and the aspect ratio of the grains. Moreover, the possibility of the small n-value even for high J(c) materials in Bi2212 is also shown.

Abstract: We have found that superconducting properties such as a critical current for bronze route Nb3Sn superconducting wires were enhanced by prebending strain (epsilon(pb)), which is the repeated bending strain at room temperature. In this study, four kinds of react and wind (R&W) processed CuNb reinforced bronze route Nb3Sn coils with epsilon(pb) = 1.0, 0.8, 0.5 and 0% were prepared. We investigated the effect of prebending strain for the coils. In the electromagnetic compressive stress condition, a critical current (I-c) of the R&W processed coil was enhanced by the prebending strain. These I-c values are larger than those of a short sample wire without prebending strain. In the hoop stress condition, the I-c of four coils revealed a similar value. Therefore, it is considered that the I-c was limited by the large tensile stress for all coils in the hoop stress states. These results suggest that the I-c enhanced by the effect of prebending strain is applicable for the R&W coil design without degradation in large stress and strain states.

Abstract: We have found that the hexagonal ZrNiAl-type compounds MnFe(P1-xGex) with x = 0.15 and 0.17 show temperature- and field-induced first-order paramagnetic-to-ferromagnetic transitions with remarkable hysteresis loops at T-C similar or equal to 250 K. The hysteresis widths in both temperature and field are much larger than those for a similar system of MnFe(P,As). On cooling below T-C, the hexagonal lattice of MnFe(P1-xGex) contracts by 1.5% along the a-axis and elongates by 2.8% along the c-axis, keeping the crystal symmetry unchanged. The very small volume expansion of less than 0.1% suggests that the first-order transition is related to the anisotropic lattice distortion rather than the volume change.

Abstract: Fundamental examinations were carried out of high strength bronze-processed Nb3Sn Wires with Ta-reinforced filaments. A long Nb3SD wire with reinforced filaments was also trial-manufactured to test its practicality and its properties were measured. It is expected that Nb3Sn wires with high strength and high critical current can be realized by reinforcing the filaments with Ta. Our series of examinations and the trial-manufacture revealed the high potential usefulness of the wire in practical applications such as in superconducting magnets fabricated using the R&W method.

Abstract: Polyaniline films were prepared by electropolymerization under a magnetic field of 5T parallel (+5T) or antiparallel (-5T) to the faradaic currents. They were used as a modified electrode and their chiral properties were examined for L-3-(3,4-dihydroxyphenyl)alanine (L-DOPA), L-ascorbic acid (L-AA) and D-isoascorbic acid (D-AA) by cyclic voltammetry. The redox currents of L-DOPA on the +5T-film electrode were smaller than those on the -5T-film electrode, and the results for racemic mixture of L-and D-DOPA were the same on the two electrodes. The oxidation current Of L-AA on the +5T-film electrode was larger than that on the -5T-film electrode, and the result for D-AA was opposite. These facts demonstrate that the two electrodes have the opposite chirality each other and possess the ability of chiral recognition. (c) 2006 NIMS and Elsevier Ltd. All rights reserved.

Abstract: The magnetic and electrical properties on magnetic Heusler alloy Ni50Mn36Sn14 were studied in magnetic fields up to 18 T in 4.2-270 K temperature range. It was found that at the vicinity of 160 K the resistivity jump of 46% is accompanied by the magnetic phase transition. Furthermore, the large magnetoresistance effect of 50% by the magnetic field induced magnetic phase transition was observed. (c) 2006 American Institute of Physics.

Abstract: To understand the underlying physical trends of the current instability in a composite high-T-c superconductor, the limiting margin of its current-carrying capacity is derived in dc magnetic fields in the framework of the macroscopic continuum approximation. A static zero-dimensional model was used to formulate the peculiarities of the nonisothermal electric field distribution in a composite in the fully penetrated current states. The power and exponential equations describing the E(J) dependences of a superconductor are used. The boundary of the allowable stable values of the electric field, current, and temperature are investigated using qualitative and quantitative models. Permissible stable values of the electric field and current, which might be lower (subcritical states) or higher (overcritical states) than those determined by the critical voltage criterion, are discussed. It is stated that the subcritical quenching electric states are more probable in the operating regimes, which are observed in the high magnetic field. The overcritical stable quantities of the electric field exist, for example, if the superconducting composite has a relatively small volume fraction of the superconductor in a composite. In the meantime, the stable current modes may be both subcritical and overcritical when the permissible value of the electric field is overcritical. As a consequence of these features, an unavoidable increase in temperature of the composite superconductor occurs before its transition to the normal state. The latter depends on a broad shape of the E(J) dependence of high-T-c superconductor and the current sharing between the superconducting core and the matrix. In the limiting case, a stable value of the composite temperature may equal the critical temperature of the superconductor. For such operating states, the criterion of the complete thermal stability condition is written taking into consideration the nonlinear character of the E(J) dependence. Simultaneously, an allowable change in temperature of the superconducting composite leads to the thermal degradation of its current-carrying capacity. It depends on the critical current density of the superconductor at bath temperature, amount of a superconductor, and cross section of a composite under fixed cooling conditions. In particular, it is shown that the currents corresponding to the instability onset do not increase proportionally with relevant increase of the superconductor�s amount. The estimates presented have general character and may be used to verify the operating states of low-T-c superconducting composite. (c) 2006 American Institute of Physics.

Abstract: Nanoscale C and SiC doped. MgB2 tapes were prepared by the in situ powder-in-tube method. The samples were characterized using X-ray diffraction, scanning electron microscope, superconducting quantum interference device magnetometer etc. Transport J(C) and its magnetic field dependence were evaluated by a standard four-probe technique. It is found that JC for all the C and SiC doped tapes was significantly enhanced in magnetic fields up to 14 T compared to the undoped ones. For the 5 % C and SiC doped samples, at 4.2 K and 16 T, JC increased by a factor of 32 and 26, respectively. The improvement of J(C)-B properties in C and SiC doped MgB2 tapes is attributed to good grain linkage and the introduction of effective flux pining centers with the doping. Furthermore, our results clearly prove that the observed positive effects after mixing with SiC are nothing else than the result of the decomposition of this compound and substitution of carbon for B in MgB2.

Abstract: We review the current status of the growth, characterization and applications of Bi-Sr-Ca-Cu-O (BSCCO) whiskers from the materials science point of view. Our analysis leads to the conclusion that reconsideration of the importance of the whisker studies is necessary; whiskers can play a major role in studies of the growth mechanism and defects, properties control and their understanding, and new devices and applications. Arguments favourable to the idea that BSCCO whiskers can possibly have a significant impact on future synthesis of nano-objects in this system or other high-T-c superconducting systems, as well as in investigation and understanding of the growth processes under elevated magnetic fields, are discussed. Emphasis is made on superconducting whiskers, but non-superconducting ones are also briefly addressed.

Abstract: Structural transformations of MnAs and MnAs0.9Sb0.1 were investigated by X-ray diffraction in high magnetic fields up to 5 T. The temperature dependence of the magnetization was measured in a magnetic field of 0.01 T and the Curie temperature T-C was determined to be 315 K for MnAs and 290 K for MnAs0.9Sb0.1 during heating process. For both compounds, a metarnagnetic transition from a paramagnetic to a ferromagnetic state was observed above T-C. The X-ray diffraction profile at 319 K for MnAs showed a single phase of an orthorhombic MnP-type structure in zero field. An applied magnetic field of 3 T induced the appearance of a hexagonal NiAs-type structure. On further increase of the magnetic field, a single phase with a hexagonal structure was realized above 3.5 T in a forcedferromagnetic state. The X-ray diffraction profile at 295 K for MnAs0.9Sb0.1 showed a hexagonal NiAs-type structure. The coexistence of ferromagnetic and paramagnetic states with different lattice parameters was confirmed in a magnetic field of 2.5 T. The volume expansion induced by a magnetic field was found to be 2.1 % for MnAs and 1.1 % for MnAs0.9Sb0.1.

Abstract: The thermal runaway phenomenon in Ag/Bi2Sr2CaCu2O8 composite conductors is studied for the nonlinear temperature and magnetic field dependences of their critical current density J(c) (T, B) and matrix resistivity pm (T, B) (nonlinear approximation). The influence of the applied magnetic field, heat transfer coefficient, matrix resistivity and volume fraction of the composite superconductor on the static thermal and electric states were investigated. The used model is based on steady heat and current balance equations. It allows us to investigate the non-isothermal voltage-current characteristic of composite superconductors, that roots the static description of their operating regimes and allows us to determine the limiting quantities of the thermal runaway parameters. It is found that there exist stable jumps of the electric field, current and temperature without the transition of the superconducting composite into the normal state. The presence of these static states is a result of the additional stable branches on the voltage-current characteristics, which appear according to the variation of the differential resistivity of a composite. The latter may have wide range fields due to the coupled thermo-magnetic and current-sharing mechanisms changing the quantities theta J(c)/ theta T and theta rho(m) / theta T. This variation takes place when the applied magnetic field or operating parameters of a composite exceed some characteristic values. As a result, the non-monotonic temperature dependence of the Joule heat release will take place. Besides, it is shown that the stable voltage (without thermal runaway) may exist when the temperature of the Ag/Bi2Sr2CaCu2O8 composite stably increases from the coolant temperature up to the critical temperature of a superconductor during current charging. The thermal runaway parameters as a function of the applied magnetic field are numerically derived accounting for the additional stable branches of the voltage-current characteristic.

Abstract: Static thermal and electric states before current instability in the current-carrying conductor like Bi-based superconducting composite are theoretically studied under the assumption that the critical current density of a superconductor and matrix resistivity are the non-linear functions of the temperature at fixed applied magnetic field. The simulation was made for the conduction-cooling conditions at different operating temperatures. The proposed analysis was based on the investigation of the non-isothermal voltage-current characteristics of composite superconductors. It is shown that they may have many-valued stable and unstable branches appearing in accordance with the non-trivial variation of the differential resistivity with increasing temperature. These states, first of all, are due to the temperature change of partial derivative J(c)/partial derivative T and are accompanied with the jump-like current-sharing mechanism. The parameters of the current instability onset as a function of operating temperature are numerically derived accounting for the additional stable branches of the voltage-current characteristics. In particular, it is revealed the existence of the static states when Bi-based composite superconductors may have a stable current distribution in the temperature range increasing up to the critical temperature of a superconductor without redistribution of all transport current into the matrix. The peculiarities of these phenomena are discussed. (c) 2005 Elsevier B.V. All rights reserved.

Abstract: High field X-ray diffraction measurement was performed on a ferromagnetic compound MnFeP0.5 As-0.5 which is recently found to be a new candidate as magnetic refrigeration materials. The compound with a hexagonal Fe2P-type structure shows a field-induced isostructural phase transformation with a hysteresis by applying a magnetic field, accompanied by the metamagnetic transition from the paramagnetic to the ferromagnetic state at just above the Curie temperature of 284 K. We found that the cell volume slightly and continuously decreases with increasing magnetic fields through the field-induced phase transition, although the lattice parameter ratio c/a drastically changes.

Abstract: Distribution of tritium concentrations on the Surface and in the bulk (up to I turn in depth) in a complete poloidal set of divertor tiles exposed to D-T plasma shots in JET was measured by beta-ray-induced X-ray spectrometry (BIXS). The observed X-ray spectra showed that tritium distribution was different not only from tile to tile but also highly non-uniform in each individual tile. The peaks of bulk tritium concentration obtained by BIXS are correlated with the corresponding one obtained previously by other methods. For the first time, tritium depth profiles in the plasma-facing surface of complete divertor tiles were obtained by BIXS and they can be classified by four types of a tritium depth profile. (c) 2004 Elsevier B.V. All rights reserved.

Abstract: Pressure dependence of infrared absorption has been measured in Cs(2)TCNQ(3) single crystals grown under magnetic field of 5 T (5 T crystals). The behavior of the C-CN as well as C-H stretching modes suggest that there occurs a phase transition which resembles to the one related to the insulator to metal transition in the crystals grown without magnetic field (0 T crystals). This transition, however, takes place at 4.1 GPa, slightly higher than the case of 0 T crystals. The charge transfer degree of the neutral and radical molecules are found to be rho = 0.30-0.37 and 0.81-0.85, respectively, which are significantly different from that of 0 T crystals. These differences are suggested to arise from the changes in the relative positions of the TCNQ molecules, as indicated from the behavior of the EMV mode. (C) 2004 Elsevier B.V. All rights reserved.

Abstract: We have studied the effect of Zr addition on the field dependence of transport J(c) for filamentary (Nd - Eu - Gd)Ba2Cu3Ox. superconductors to enhance the flux pinning. We prepared the filamentary (Nd0.33Eu0.38Gd0.28)Ba2Cu3OxZry (y = 0, 0.001, 0.002) precursors by a solution spinning method. The precursor was partially melted in flowing 0.1%O-2 + Ar under various heating conditions to obtain high J(c) value. The optimum heating condition was dependent on sample diameter. A maximum J(c) value of 3 x 10(4) A/cm(2) at 77 K and self-field was attained for the sample with 0.001 at% Zr. The samples had well aligned texture along the filament diameter as well as the length. The J(c) was measured at 77 K in applied magnetic fields up to 14 T by rotating the sample along the direction perpendicular to the filament length. Anisotropic behavior of the field dependence of J(c) was detected. Although the J(c) values measured at the optimum angle for the samples with 0.001 at% Zr decreased with increasing the applied fields above 10 T, the J(c) values for the Zr addition samples were higher than that for the non addition sample by applying the fields up to 11 T.

Abstract: A 19 T cryocooled superconducting magnet with a 52 mm room temperature bore is currently under construction. The magnet consists of an outer NbTi section, middle Nb3Sn section and innermost high-T-c section., The coils are exposed to an electromagnetic hoop stress following the magnetic field generation. In this 19 T cryocooled superconducting magnet, the high-T-c coil windings are Bi-2223 tapes with a low matrix ratio. Because of this, the mechanical characteristics, i.e., stress-strain characteristics, stress/strain dependence of the critical current and bending strain dependence of the critical current, were explored for the Bi-2223 tape. Furthermore, the small coil was wound with the superconducting tape. It was tested under magnetic fields to examine the stress-strain characteristics caused by the electromagnetic hoop stress.

Abstract: We report on the annealing effects on the microstructure, electrical, and magnetic properties of jelly-rolled Cu-xvol %Nb (x = 25, 33, 50, 63) composite wires, a promising material to be used in high-field magnets. During annealing at temperatures as high as 850 degreesC, noticeable changes take place in the microstructure, including recovery and recrystallization of copper and niobium, followed by partial spheroidization and further coarsening of niobium filaments. The influence of these microstructural changes on the electrical and magnetic properties of jelly-rolled Cu-Nb composite wires is discussed.

Abstract: Polyaniline film electrodes were prepared by a magnetoelectropolymerization (MEP; electropolymerization under magnetic fields) method, and their chiral electrode properties were examined for L- and D-ascorbic acids by cyclic voltammetry. The MEP film electrodes showed different oxidation currents between enantiomers, and those prepared under reverse magnetic 4-fields showed opposite chirality. These results indicate that the MEP method introduces chirality to the polyaniline films and Such film electrodes possess the ability of enantioselective recognition for ascorbic acid.

Abstract: We have found that prebending treatment, which is repeated bending load at room temperature, greatly enhances the critical current, upper critical field and critical temperature of practical Nb3Sn superconducting wires. In this paper, we focus on the application of the prebending strain effect to practical superconducting coils fabricated by a react-and-wind method. To demonstrate the prebending strain effect on the react-and-wind coil, we prepared two kinds of CuNb/Nb3Sn superconducting monolayer coils. For one of the coils, the superconducting wire of 1.0 mm diameter was repeatedly bent by using ten fixed pulleys before the winding process, resulting in a prebending strain value of 1.0%. The final winding diameter of both coils was 200 mm and the number of turns was 49. In the compressive stress condition, the critical current of the coil with 1.0% prebending strain was 296 A at I I T, which was larger than that of the coil with 0% prebending strain. These values were much larger than the critical current of the witness sample. The results indicate that the prebending treatment enhanced the coil critical current. In the case of the hoop stress condition, the coil critical currents were approximately 230 A at I I T for both coils. The maximum electromagnetic hoop stress was calculated to be 360 MPa. The short sample tensile test results qualitatively explained the critical current deterioration of the coil. Furthermore, the 360 MPa hoop stress did not deteriorate the critical current irreversibly.

Abstract: Sodium tellurite glass was evaporated by irradiating a CO2 laser beam under a high magnetic field with a large ggadient. Glass microspheres were formed as a cloud of soot with the condensation of the vapor from the source glass. The flow of the glass soot due to thermal convection was observed when the glass source was evaporated under a zero field, but was suppressed by applying the high magnetic field with a large gradient, which reduces gravity for the glass by a magnetic force of -0.8g in the gravitational scale. The maximum size of the microspheres decreased to about half that of microspheres formed under a zero field. Sodium concentration in the microspheres was found to increase with magnetic field. A disturbance of the motion of evaporated species due to electromagnetic force was suggested as an origin of the suppression of recondensation to the surface of source glass melt under the high magnetic field, resulting in the increase in the sodium concentration of the microspheres and in the decrease in their size.

Abstract: Carbon nanohorn (CNH) doping in MgB2 wire prepared by suspension spinning was studied to enhance flux pinning. The mixed powders of MgB2 and CNH with nominal composition of (MgB2)(0.95)C-0.05 were suspended in a mixed poly(vinyl alcohol) solution. The as-drawn filaments were hot-pressed under 20 MPa at 200 degrees C for 8 h. The samples were enveloped by an iron sheet with a pellet of mixed powder of Mg and B and vacuum-sealed in a fused quartz tube, and then sintered at the temperature ranging from 885 degrees C to 900 degrees C for 2-3 h. The superconductivity of the samples was studied by electrical resistivity and SQUID method. Serious deterioration of T, was not observed for the doped sample. The CNH doping resulted in enhancement of the transport J(C) values at 4.2 K in high fields ranging from 6 T to 10 T by sintering at 885 degrees C for 2 h. The superconductivity at 4.2 K was maintained by applying the field of 14 T for the doped sample sintered at 900 degrees C for 3 h. (c) 2005 Elsevier B.V. All rights reserved.

Abstract: Fe-sheathed tapes of MgB2 with addition of SiC have been prepared by the powder-in-tube (PIT) method using a powder mixture mechanically milled in an argon or hydrogen atmosphere. The reactivity of the component powders in the mixtures, Mg, B and SiC, was significantly enhanced by mechanical milling, so that MgB, formed faster than in tapes fabricated from a hand-milled mixture. At the same time the number of impurity phases was higher, and the impurity phases of Mg2Si and Fe2B were observed only in these tapes. Mechanical milling also induced a lower quality of MgB2, especially for tapes produced from powders milled in a hydrogen atmosphere, with a significant influence on the values of the critical temperature T-C and critical field, J(C). (c) 2005 Published by Elsevier B.V.

Abstract: The method of critical current measurement in a magnetic field using a DC transport current has been developed for bulk superconductors. The measurement of the critical current, I,, up to 50 A at a temperature of 77 K became possible by reducing thermal and mechanical stresses caused in the sample due to rapid cooling from the room temperature to 77 K and a electromagnetic force (Lorentz force), etc. The critical current of 50 A is reduced into 14,000 A/cm(2) of critical current density, J(c), with a cross section of 0.0035 cm(2). The magnetic field dependence of J(c) was investigated from 1 T to 10 T for (Nd0.33Eu0.38Gd0.28)Ba2Cu3Oy bulk superconductors. The magnetization measurement was performed for the sample cut out from the same part of the same crystal as that used for the transport measurement of I., from which the critical current density was also estimated. In low magnetic fields, the magnitude of critical current density obtained by the transport method, J(c)(T), was larger than that estimated from the magnetization, J(c)(M). This result reflects the difference of criterion to determine the value of J(c)(T) and J(c)(M). In higher magnetic fields, however, it was observed that J(c)(T) was smaller than J(c)(M) and the irreversibility field estimated from J(c)(T)-B curve is slightly lower than that given by the magnetic hysteresis. When the external magnetic field was applied, anomalous voltage peaks in the I-V curve were observed below I-c(T), which may be caused by the sample slightly moving by the Lorentz force. (c) 2005 Elsevier B.V. All rights reserved.

Abstract: The magnetic field effect on the structural property of a ferromagnetic compound MnFeP(0.5)AS(0.5) was investigated by powder X-ray diffraction measurement in magnetic fields up to 5 T. The compound with the hexagonal Fe2P-type structure shows a field-induced isostructural transformation with a hysteresis by applying magnetic field, accompanied by the metamagnetic transition from the paramagnetic to ferromagnetic state just above the Curie temperature of 284 K. In this transformation, the a parameter expands by 0.5% whereas the c parameter contracts by 1%. However, the cell volume slightly and continuously decreases with increasing magnetic field through the transformation.

Abstract: Recently, a strong cathodoluminescence at 215 nm (photon energy 5.765 eV) has been reported on pure HPHT hexagonal boron nitride (hBN) single crystals (K. Watanabe et al., Nature Mater. 3, 404 (2004)). For the first time, we measured the photocurrent and optical absorption spectra of these new hBN crystals in a broad spectral range 1-6.6 eV. Our measurements support the previously published results, especially that the single crystal hBN has a direct band gap about 5.95 eV, and a rather strong exciton binding energy that allows excitons to exist even at room temperature. We found three new opto-electronic transitions at 2.7, 3.6 and 5.4 eV and observed the oscillatory photoconductivity in 2.7-3.6 eV region. (c) 2005 WILEY-VCH Vertag GmbH & Co. KGaA, Weinheim.

Abstract: Magnetic measurements on Ni2-xCuxMnGa with 0 <= x <= 0.8 are made in the temperature range between 4.2 K and 440 K. A phase diagram of Ni2-xCuxMnGa is determined from the results of the temperature dependence of the initial permeability. The Curie temperature T-C increases with the Cu concentration x. The martensitic and reverse martensitic transformation temperatures decrease abruptly with x. It is deduced that the substitution for Ni by Cu in Ni2MnGa promotes to localize the magnetic moment of Mn atom.

Abstract: We prepared filamentary 0.1 at% Zr-doped (Nd0.33Eu0.38Gd0.28)Ba2Cu3Ox superconductors by solution spinning and partial melting in flowing 0-1% O-2 + Ar gas. The transport critical-current density (J(c)) was measured at 77 K in applied magnetic fields up to 14 T by rotating the sample along a direction perpendicular to the filament length. Anisotropic behavior of the field dependence of J(c) was detected by applying a field of more than 4 T. The J(c) values for the Zr-doped sample were higher than those for the undoped sample on the application of fields of up to 11 T. The J(c) values measured at the optimized angle for the doped sample were more than 10(5) A/cm(2) at 77 K by applying fields of up to 6 T. Transmission electron microscopy (TEM) of the sample was performed using an ultra high-voltage TEM to clarify the pinning centers. Intergrowth of 124 phase and stacking faults in the oriented 123 matrix were observed both for the doped and undoped samples. Zr doping resulted in the fluctuation of the structure with a short disorder range of 10-30 nm. A modulated structure and fine twin planes crossing each other were partly observed for the doped sample. The presence of such small-scale disorder could improve flux pinning in the middle field region. (c) 2005 Elsevier B.V. All rights reserved.

Abstract: Magnetovolume effect due to the itinerant-electron metamagnetic (IEM) transition in La(Fe0.88Si0.12)(13) has been investigated by x-ray diffraction measurements in high magnetic fields. No crystal structure change was confirmed after the IEM transition. The relative change in the lattice constant measured perpendicular to the magnetic field direction is similar to the longitudinal linear magnetostriction, and hence the volume change due to the IEM transition is isotropic. The volume change in both the ferromagnetic and the paramagnetic states is proportional to the square of the magnetization, though the magnetovolume coupling constant in the former is smaller than that in the latter. (C) 2004 American Institute of Physics.

Abstract: It is recognized that the strain in Nb3Sn conductors is a serious problem, because it suppresses superconducting properties. We have proposed that prebending treatment, which means repeated bending loads, is one of the ways to control the strain state. The upper critical field and the critical temperature were examined for the prebent. Nb3Sn wires. We found that the enhancement of the upper critical field from 23.7 T to 25.2 T at 4.5 K and the enhancement of the critical temperature from 17.4 K to 17.9 K were achieved for the CuNb-reinforced Nb3Sn wire by applying the prebending strain. Since these values are similar to those of the strain-free Nb3Sn bulk, the strain state of the wires is definitely optimized by the prebending treatment.

Abstract: Several types of reinforced Nb3Sn wires have been developed to prevent reduction of superconducting properties by applying a strong electromagnetic force. To fabricate a cryocooled magnet using those reinforced wires, we experimentally measured the minimum quench energy (MQE) under cryocooled conditions of some reinforced Nb3Sn wires. As a result, it became clear that thermal stability expressed as MQE was controlled by the temperature margin between the temperature of the operating condition and the transition temperature from superconductivity to normal. Using the FEM analysis, it was realized that the cause of the decline in thermal stability for the reinforced wires was the low thermal conductivity of the reinforced materials. (C) 2004 Elsevier Ltd. All rights reserved.

Abstract: The magnetic and structural properties of Ce(Fe0.9Co0.1)(2) with the C15 cubic Laves-phase structure have been studied by magnetization measurement in high magnetic fields under high pressures, and powder X-ray diffraction measurement in fields up to 5 T. The C15 cubic structure is distorted to rhombohedral symmetry accompanied with the magnetic phase transition from the ferromagnetic to the antiferromagnetic state, which recovered the C15 structure by applying the magnetic field. The antiferromagnetic phase is induced by the lattice contraction due to hydrostatic pressure. Obtained results suggest that the AFM correlation due to the Cc 4f-Fe 3d hybridization plays an important role on the structural and magnetic properties. (C) 2004 Elsevier B.V. All rights reserved.

Abstract: Cyclotron resonance (CR) measurements on single crystals of GdSb have been performed in the frequency range from 50 to 110 GHz. By using the high-quality crystal with the residual resistivity ratio of about 500, two CR absorption lines are observed at low temperatures for B\textbackslash\textbackslash[0 0 1]. The effective mass values are estimated to be 0.261m(0), and 0.50m(0), respectively. (C) 2003 Elsevier B.V. All rights reserved.

Abstract: The magnet technology at the High-Field Laboratory for Superconducting Materials (HFLSM) contributed to the success of the world�s first practical cryogen-free superconducting magnet. A new project of a cryogen-free 19 T superconducting magnet with a 52mm room temperature experimental bore has started. A B(i)2Sr(2)Ca(2)Cu(3)O(10) high-temperature superconducting insert coil is to be employed. In the magnetic field application for materials development, magnetic levitation has been demonstrated using a cryogen-free hybrid magnet. Up to now, the cryogen-free 21.5 T hybrid magnet is easily operated for a container less melting experiment. In addition, a cryogen-free 30 T hybrid magnet is now being constructed at the HFLSM. (C) 2004 Published by Elsevier B.V.

Abstract: This paper describes a design of a cryocooler-cooled 19 T superconducting magnet. The technical features of the magnet are a Bi2223 insert coil composed of 25 double pancake coils, Nb3Sn coils using a Nb3Sn wire reinforced with Nb-Ti-Cu compound, and a cooling structure using two types of cryocoolers. Coil protection from quenching was confirmed by numerical analysis. A preliminary experiment was carried out in order to investigate the influence of the bending strain upon a maximum permissible hoop stress of Ag-sheathed Bi2223 tape conductor.

Abstract: Structural transformation induced by magnetic fields on MnAs and MnAs0.9Sb0.1 was investigated by the X-ray diffraction measurements in high magnetic fields up to 5 T. The X-ray diffraction profiles at 319 K for MnAs showed a single phase of the orthorhombic MnP-type structure in zero field, and applying a magnetic field of 3 T caused an appearance of the hexagonal NiAs-type structure. On further increase of magnetic fields, the single phase with the hexagonal structure was confirmed above 3.5 T in a forced ferromagnetic state. The X-ray diffraction profiles at 295 K for MnAs0.9Sb0.1 showed the hexagonal NiAs-type structure. However, the coexistence of two kinds of the NiAs-type structure with different lattice parameters was confirmed in the magnetic field of 2.5 T. The two phase coexistence was also confirmed in the temperature variation measurements in zero magnetic field. The lattice volume of the ferromagnetic phase was 1.1% larger than that of the paramagnetic phase. These results imply that the transition at T-C for MnAs0.9Sb0.1 is of the first-order.

Abstract: We have studied the magnetic and structural properties of Ce(Fe0.9Co0.1)(2) with the C15 cubic Laves-phase structure by low-temperature x-ray diffraction measurements in magnetic fields up to 5 T, and in the temperature range from 9 to 300 K. The C15 structure is distorted to rhombohedral symmetry at 90 K in zero magnetic field, accompanied with the magnetic phase transition from the ferromagnetic (FM) to the antiferromagnetic (AFM) states with decreasing temperature. In the AFM state, it is observed clearly that the rhombohedral distortion state recovers the C15 structure by applying magnetic field, accompanied with the metamagnetic transition from the AFM to the forced FM states with a hysteresis in the magnetization process.

Abstract: The structural phase transition induced by magnetic fields on MnAs was observed by the X-ray diffraction measurements in high magnetic fields up to 4 T. Magnetization measurements showed that Curie temperature T-C was 315.5 K for increasing temperatures and a metamagnetic transition from the paramagnetic to the ferromagnetic state occurred above T-C. The structural transformation from the hexagonal NiAs-type to the orthorhombic MnP-type structure was confirmed at T-C with increasing temperature from 290 to 319 K via two-phase coexistence region. The X-ray diffraction profiles at 319 K showed the single phase of the MnP-type structure in zero field and applying magnetic field of 3 T caused appearance of the Brag peak of the hexagonal structure. On further increase of magnetic fields, the single phase of the hexagonal structure was observed above 3.5 T in the forced ferromagnetic state. Both the magnetic and structural transitions induced by magnetic fields above T-C were first order with a hysteresis and had a close relationship between each other. (C) 2004 Elsevier B.V. All rights reserved.

Abstract: The two-legged spin ladder NH4CuCl3 has a gapless ground state and shows two-step plateaus in the magnetization curve. The temperature dependence of the Cu-NMR resonance shift measured around 14.7 T shows a clear kink at 4 K. This is considered as the evidence for the field-induced magnetic order proposed by Kurniawan et al. (C) 2004 Published by Elsevier B.V.

Abstract: We have performed the magnetization and X-ray diffraction measurements on Mn3Ga1-xAlxC (0 <= x <= 0.1) with a perovskite-type structure in the temperature T range from 5 to 400 K to investigate the behavior of the complicated magnetic phase transitions. The obtained results suggest that the crystallographic character is closely correlated to the magnetic properties. The new magnetic phase diagram of this system is presented, which indicates the two-phases coexistence in Mn3Ga1-xAlxC at lower temperature. (C) 2003 Elsevier B. V. All rights reserved.

Abstract: The influence of columnar defects introduced by the heavy-ion irradiation on the pinning parameters in YBa2Cu3O7-delta thin films was investigated. The pinning parameters n, J(cm) and DeltaJ(c) were derived by fitting the experimentally obtained E-J characteristics to the theoretical curves calculated from the percolation transition model. The values of n and J(cm) have been increased and the value of DeltaJ(c), has been decreased by the introduction of columnar defects. (C) 2004 Elsevier B.V. All rights reserved.

Abstract: To understand the basic mechanisms of the thermal runaway phenomenon, the limiting margin of the current instability, which may spontaneously occur in composite high-T-C superconductors like multifilament Bi-based wire or tape, is derived under DC magnetic field. The current sharing and allowable temperature rise effects were considered. A static zero-dimensional model was utilized to describe the basic formulae dealing with the peculiarities of the non-isothermal change of superconducting composite voltage-current characteristic. The boundary of allowable stable values of the temperature, electric field and current are derived analytically. It was shown that permissible values of the current and electric field might be higher than those determined by use of the standard critical current criterion. In consequence of this feature, the noticeable allowable temperature rise of the composite superconductor before its transition to the normal state may be seen. The criterion for complete thermal stability condition is written describing the state when temperature of the composite equals critical temperature of a superconductor and the transport current flows stably only in matrix. The performed analysis also proves the existence of value of the volume fraction of a superconductor in composite at which its current-carrying capacity has minimum. These peculiarities are due to the stable current redistribution between superconductor and stabilizing matrix. Therefore, the current sharing not only leads to the matrix/superconductor ratio effect on the stable operating characteristics of the composite high-T-C superconductors but also becomes important in the adequate description of quench process in the high-T-C superconducting magnets. (C) 2004 Elsevier B.V. All rights reserved.

Abstract: Terahertz (THz) radiation from femtosecond-laser-irradiated InAs (100) surface is investigated. It is found that THz-radiation spectrum exhibits two inter-related phenomena in a strong magnetic field under the Voigt configuration. The peak shift of THz-radiation spectrum toward lower frequency is observed with increasing magnetic field. Additionally, THz-radiation spectrum is found to posses a periodic structure owing to the interference of THz-radiation pulses from the front and back surfaces of the InAs substrate. The physical origin of the latter phenomenon is discussed by considering the magneto-plasma effect, which affects both real and imaginary parts of refractive index for THz-radiation propagating in a direction perpendicular to the magnetic field.

Abstract: The structural transformation of a ferromagnetic Mn1.07CO0.92Ge compound was studied by magnetization measurement in magnetic fields up to 13 T and powder X-ray diffraction measurement in fields up to 5 T. The Curie temperature is determined to be 275 K. At room temperature, the compound has a hexagonal Ni2In-type structure, and it transforms diffusionlessly into an orthorhombic TiNiSi-type structure at Ms = 210 K with hysteresis. The cell volume expands by 5.3% and the magnetic moment increases by 24% at Ms, accompanied with this martensitic structural transformation. In addition, we confirmed for the first time that magnetic field induces the structural transformation in Mn1.07Co0.92Ge at the vicinity of Ms.

Abstract: The formation and texture of Bi-2223 phase during sintering in a temperature gradient were investigated. Co-precipitated powders with the composition of Bi:Pb:Sr:Ca:Cu = 1.85:0.35:1.90:2.05:3.05 were used. Samples set on a silver holder were sintered at 850 degreesC for 120 h in a vertical tube furnace with a temperature gradient of 15 degreesC/cm installed in a solenoid-type superconducting magnet. A vertical magnetic field can be applied parallel to the long axis of the furnace. It has been found that the Bi-2223 grains with their c-axis parallel to the axial direction of the vertical tube furnace are formed not only on the surface, but also in the center of the sample sintered at 850 degreesC for 120 It in 15 degreesC/cm temperature gradient without magnetic field. Moreover, the sample sintered in the temperature gradient and in a 10 T magnetic field have a stronger c-axis alignment of Bi-2223 phase. It is suggested that both the temperature gradient and magnetic field during sintering are favorable for the c-axis alignment of Bi-2223 phase. (C) 2004 Elsevier B.V. All rights reserved.

Abstract: The current-carrying capacity of the Ag/Bi2Sr2CaCu2O8 multifilament conductor is studied in detail as a function of the heat transfer coefficient, resistivity of the matrix, and volume fraction of the superconductor. The thermal runaway parameters corresponding to the irreversible superconducting-to-normal transition are derived analytically under the aspect of possible finite temperature rise of the composite conductor before thermal runaway. The static analytical model determines the thermal runaway parameters. The power law describes the voltage-current characteristic of a superconductor with a linear temperature dependence of the critical current (linear approximation). The performed analysis reveals that the allowable magnitude of the current and electric field before the thermal runaway may be higher than those determined by the criterion E-c = 10(-6) V cm(-1) in many practical cases. The condition of the stable state for the over-critical current is formulated and the peculiarities of such operation regimes are discussed. It is shown that the essential stationary overheating of the superconductor may occur before the thermal runaway. The minimum value of the current at which the thermal runaway starts is found if the volume fraction of superconductor in the composite is changed.

Abstract: Specimens of V-4Cr-4Ti alloy were heated at 1273 K in vacuum, and the influence of this heat treatment on H-2 absorption was examined at temperatures from 523 to 1023 K under the presence of water vapor of 10(-5) Pa. The rate of H2 absorption was significantly reduced by the heat treatment in the temperature range examined. Such reduction in the absorption rate was ascribed to the surface segregation of Ti and increase in surface oxygen coverage caused by preferential oxidation of segregating Ti by water vapor. Comparison with data reported by other researchers [J. Nucl. Mater. 233-237 (1996) 376; Fusion Technol. 34 (1998) 868; J. Nucl. Mater. 233-237 (1996) 510] indicated the strong barrier effect of Ti oxide against hydrogen ingress. (C) 2004 Elsevier B.V. All rights reserved.

Abstract: We have prepared fine filamentary EuBa2Cu3Ox superconductors by solution spinning and melt processing to fabricate the high-T-c superconducting wire with high-critical current density (J(c))at 77 K and high-magnetic fields. The filamentary precursor was partially melted in flowing 0.1% O-2 + Ar and then oxygenated. The samples in diameter of 55 mum had well aligned texture along the filament diameter as well as the length. The T-c value of the sample was 90K. The transport J(c) for the samples was measured at 77K in applied magnetic fields up to 14T by rotating the sample in a direction of the filament diameter. Anisotropic behaviour of the field dependence of J(c) along the filament diameter was detected. The sample rotated the optimized angle exhibited the highest J(c) value of 11,000 A/cm(2) at 77K and 14T. The transmission electron microscopic image for the filamentary EuBa2Cu3Ox superconductors was observed by using ultra high-voltage transmission electron microscope to clarify the pinning center. Intergrowth of 124-phase and nanoscale particle in the orientated 123 matrix were observed. The presence of such small-scale disorders could improve flux pinning at high fields. (C) 2004 Elsevier B.V. All rights reserved.

Abstract: Superconducting whiskers of Bi-2212 have been grown by an airtight crucible method in elevated magnetic fields, up to 10 T. Growth behavior with and without application of a magnetic field, as well as the SEM detailed study of the growth defects of the whiskers allow to emphasize some aspects of the growth mechanism. The conclusion is that whiskers are growing mainly through continuous crystallization at the base-end and from the so-called �micro-crucible� formed by the glassy or powdered substrates. The supply of cations by a vapor transfer is very probable, but is taking place to the micro-crucible reaction site rather than to the droplet, as in the classic vapor-liquid-solid (VLS) growth mechanism. Therefore, whiskers grow by a modified VLS-microcrucible mechanism (MVLS-MC). Application of magnetic fields during growth has proven to be a powerful tool to investigate and influence some processes. Observation of stoichiometric Bi(Pb)-2212, CuO and Ca2CuO3 whiskers is also reported. (C) 2004 Elsevier B.V. All rights reserved.

Abstract: In high temperature superconductors, a low resistivity state is quite stable from a viewpoint of power application. When a low resistivity state instead of the superconductivity with zero resistance is concentrated on, a current-carrying limitation before thermal runaway has to be investigated for high temperature superconductors. We have examined the thermal runaway parameters related to the beat transfer coefficient and the matrix resistivity for Ag-sheathed Bi2Sr2CaCu2O8 tape. The calculated parameters were evaluated in comparison with the experimental results obtained under the cryocooling condition.

Abstract: Vertical magnetic fields up to 15 T were applied to the magnetic melt-processing (MMP) of Bi2212 bulks and Ag-sheathed tapes with a core thickness above 80 mum, which were set horizontally. Texture with the c-axis along the direction of magnetic field applied during MMP is developed due to the anisotropy in magnetic susceptibility of Bi2212. The degree of texture and the anisotropy factor in magnetization increase almost linearly as the magnetic field strength H-a during MMP is increased. The anisotropy factor in magnetization reaches 6.5 at a H-a of 13 T for Ag-doped Bi2212 bulks, whereas for Bi(Pb)2212 in which Pb partially substitutes for Bi the factor is suppressed to a half of that of Ag-doped Bi2212. The transport critical current I-c and the critical current density J(c) of Bi2212 tapes also increase with increasing H-a due to the texture development and I-c reaches above 1000 A in self-filed for the tapes with a core thickness of 180 mum. However, for further thicker tapes, I-c decreases. The suppressions in the I-c for the tapes and in the anisotropy factor in magnetization for Bi(Pb)2212 bulks are due to inhomogeneous melting, and inhomogeneous nucleation and growth of crystals during MMP. When crystal growth is restricted, crystal alignment is suppressed. (C) 2002 Elsevier Science B.V. All rights reserved.

Abstract: Fatigue behavior at room temperature and its influence on critical current at 4.2 K and residual strength at room temperature of multifilamentary Nb-Ti/Cu superconducting composite wire with a filament volume fraction of 0.49 (copper ratio of 1.04) were studied. The fatigue crack nucleated in the copper in the circumferential region and propagated stably into the inner region, causing fracture of the Nb-Ti filaments in the late stage of the fatigue life. Once the fracture of the filaments started, the number of the fractured filaments increased steeply with increasing number of stress cycles, and correspondingly, the current-transportable and stress-carrying capacity of the composite decreased steeply. In this process, both the critical current and residual strength of the fatigued composite decreased nearly linearly with decreasing fraction of surviving filaments. Thus, the critical current of the fatigued composite was proportional to residual strength as a first approximation. (C) 2003 Elsevier Science Ltd. All rights reserved.

Abstract: The magnetic-field dependence of THz-radiation power from InAs surface is investigated by using a hybrid magnet, which is capable of providing a magnetic field up to 28 T. It is found that THi-radiation power saturates at approximately 3 T and also at 13 T. The maximum THz-radiation power with a high-frequency component spectrum is observed at 3 T. This result leads to the conclusion that a magnetic field of 3 T is optimum for the enhancement of THz-radiation power. Additionally, the THz-radiation spectrum exhibits a periodic structure at magnetic fields above 12 T. This can be attributed to the change in dielectric constant induced by the strong magnetic field resulting in the interference of THz-radiation pulses from the front and back surfaces of the InAs substrate.

Abstract: Various kinds of cryogenfree superconducting magnets such as a wide bore 8 T, a split-pair 5 T, and a high magnetic field 15 T magnet have been developed successfully at Tohoku University. A cryogenfree 23 T hybrid magnet composed of a cryocooled outer superconducting magnet and a water-cooled inner resistive magnet is being tested for the first time. Further, new construction projects of a cryogenfree 30 T hybrid magnet and a cryogenfree 19 T superconducting magnet have just started. (C) 2003 Elsevier Science B.V. All rights reserved.

Abstract: It has been found that the coexistence of high-temperature ferromagnetic (FM) and low-temperature antiferromagnetic (AFM) phases was observed below the charge-order transition temperature T,. for a Nd0.5Sr0.5MnO3 powder sample. In order to investigate details of the phase segregation, the X-ray diffraction was carried out for the Nd0.5Sr0.5MnO3 single crystal in magnetic fields up to 5 T. It was found that the phase segregation is strongly depends on the wave length of X-ray. These results suggest that the phase segregation of FM and AFM mainly occurs near the surface within a few gm in depth. (C) 2003 Elsevier Science B.V. All rights reserved.

Abstract: X-ray diffraction measurements on Ce2Fe17 have been performed in the temperature range from 8 to 300 K at the magnetic fields up to 5 T. The thermal expansion curves along the principal axes for antiferromagnet and ferromagnet Ce2Fe17 are presented. A distinct lattice expansion was observed simultaneously with the metamagnetic transition. This suggests that the hybridization between Fe 3d- and Cc 4f-electrons in Ce2Fe17 is suppressed by the application of magnetic field. (C) 2003 Elsevier Science B.V. All rights reserved.

Abstract: Heat transfer in water was visually observed using a liquid-crystal sheet with thermochromism under strong gradient magnetic fields. Upward thermal convection was significantly suppressed by the magnetic force, however, it remained to a small extent even under magnetic levitation conditions with a gradient field of B(dB/dz) = 1360 T-2.m(-1) C. A thermal conduction state without convection was realized under a stronger gradient field of B(dB/dz) = 2880 T-2.m(-1) at 35-40degreesC, and surprisingly the downward magnetic convection was observed under the same field at 40-45degreesC. The temperature dependence of the magnetic susceptibility of water is responsible for the convection behavior in the gradient, fields. [DOI: 10.1143/JJAP.42.L715].

Abstract: We report on the terahertz radiation from femtosecond-laser-irradiated indium arsenide in high magnetic fields up to 14 T. It is found that the radiation power exhibits anomalous magnetic-field dependence, including saturation, decrease, and recovery up to 14 T. Moreover, the radiation spectrum possesses a clear periodic structure over 6 T. (C) 2003 American Institute of Physics.

Abstract: In order to reduce thermal inputs through many measuring copper leads, we intended to fabricate a measuring leads unit using very fine YBa2Cu3O7 filaments. The long YBa2Cu3O7 filaments were prepared by a textile fiber spinning method for the oxide precursor. The 60 filaments with a size of 100 mum in diameter and 60 mm in length were attached onto three fiber-reinforced polymers, and were covered with epoxy resin. Both ends of the YBa2Cu3O7 filament were soldered with pin connectors through copper leads with 0.1 mm in diameter. The YBa2Cu3O7 measuring leads unit of 60 terminals was cooled by a pulse tube cryocooler. The newly developed YBa2Cu3O7 measuring leads unit demonstrates the extremely small heat loads of 1/10 in comparison with conventional copper measuring leads. (C) 2002 Elsevier Science B.V. All rights reserved.

Abstract: We are now constructing a cryogenfree 23 T hybrid magnet at the High Field Laboratory for Superconducting Materials, Institute for Materials Research, Tohoku University. At present, an outer section coil employing NbTi multifilamentary Wires for a cryogen,free superconducting magnet of the hybrid magnet wag combined with an inner 15.5 T water-cooled resistive magnet, and was tested as the world�s first cryogenfree hybrid magnet., The NbTi coil With 491 mm inner diameter and 584 mm outer diameter generated 4.59 T at 198 A, and the central magnetic field of 20.0 T was generated in a 52 mm room temperature experimental bore. The magnetic force field of 2030 T-2/m was obtained, and a piece of paraffin was levitated at 1200 T-2/m. Using a CO2 laser combined with the cryogenfree hybrid magnet, a containerless melting experiment in magnetic levitation was demonstrated easily for paraffin.

Abstract: Mn-55 nuclear magnetic resonance (NMR) measurements have been carried out on an oriented powder sample of Mn12 clusters in order to investigate microscopically the inner spin structure and spin dynamics of the molecule in its high-spin S=10 ground state. The external magnetic-field dependence of Mn-55-NMR spectrum up to 15 T gives a direct confirmation of the internal magnetic structure of the Mn12 cluster, in which spin moments of Mn4+ (S=3/2) ions are polarized antiparallel to that of Mn3+ (S=2) ions. It is proved that the microscopic spin configuration rotates rigidly when an external magnetic-field is applied perpendicular to the easy axis. When the magnetic-field is applied parallel to the easy axis of the Mn12 cluster, the nuclear-spin-lattice relaxation rate 1/T-1 decreases as expected from the field dependence of the lifetime broadening of the low-lying sublevels due to spin-phonon interaction. On the other hand, for transverse fields 1/T-1 increases with H displaying a broad maximum at H=5-6 T. This behavior can be accounted for only in part by spin-phonon interaction. The dominant contribution to 1/T-1 for transverse field is shown to arise from quantum fluctuations of the component of the magnetization transverse to the nuclear Zeeman quantization axis.

Abstract:

Abstract: The influence of magnetic field on the crystallization process has been examined in Cs(2)TCNQ(3) (TCNQ = tetracyanoquinodimethane), a strongly Coulomb-correlated organic semiconductor. The crystal structure is unaffected by the magnetic field, while the electric, magnetic and optical properties change markedly if the magnetic field higher than a threshold (similar to4 T) is applied during the crystal growth. The high-field crystals exhibit a very weak but distinct spontaneous magnetization with the exceedingly high Curie temperature of similar to420 K. The infrared and visible spectroscopy data show that this novel ferromagnetism concurs with the renormalization of the pi* state of TCNQ radical anions, TCNQ(-). (C) 2002 Elsevier Science B.V. All rights reserved.

Abstract: Cyclotron resonance (CR) measurements on a single crystal of PrSb have been performed at temperatures between 1.5 K and 20 K in the frequency range from 50 to 110 GHz. Three CR absorption lines are observed at low temperatures. For magnetic fields parallel to the [001] direction, the determined effective masses are 0.25m(0), 0.31m(0), and 0.53m(0), respectively. In addition to �normal� CR, we have observed Doppler-shifted cyclotron resonance which shows nonlinear behavior on the frequency-field diagram.

Abstract: The development of a cryogen-free hybrid magnet with no use of liquid helium was intended. A cryogen-free hybrid magnet is composed of an outer conduction-cooled superconducting magnet using GM-cryocoolers and an inner water-cooled resistive magnet. As a first step, we constructed a cryogen-free NbTi superconducting magnet with a 360 mm room temperature bore, which generated 4.5 T at a magnet center. The thermal stability concept of the critical current margin is adopted for magnet design. A 20 T static magnetic field and a magnetic force field corresponding to 2030 T-2/M by combining with the 15.5 T water-cooled magnet were obtained. A container-less melting experiment was carried out using a newly developed 20 T cryogen-free hybrid magnet. A great interest is focused on Marangoni convection in container-less melting. Thermocapillary convection known well as Marangoni is being investigated in the non-gravity state due to high magnetic fields, using the world�s first cryogen-free hybrid magnet. (C) 2002 Elsevier Science B.V. All rights reserved.

Abstract: X-ray diffraction measurements under high and low temperature, and magnetic field have been performed for the doped La1-xCaxMnO3+delta polycrystals to clarify the coexistent phases and their structures around the composition of x similar to 0.5. By measurements at high temperature, the transition from a Pnma to an Imma space group symmetry phase has been firstly observed in this system at the temperature between 500degreesC and 600degreesC. At low temperature, the importance of the measurement of (131) reflection is noticed and the phase fraction of two similar Pnma phases with ferromagnetic and anti-ferromagnetic states is determined. It is found that the application of the magnetic field by 5 T and the slight change of the composition x by 0.02 remarkably affect this phase fraction.

Abstract: Materials synthesis processes in high magnetic fields are investigated for high-T-c superconductors at the High Field Laboratory for Superconducting Materials, Institute for Materials Research, Tohoku University. On a melt growth process of YBa2CU3O7 bulk in magnetic fields, it was found that the crystallinity is improved. These results are due to not only the magnetic field orientation but also the decrease of the crystal growth rate by the magnetic field, which is suggested from a differential temperature analysis measurement in magnetic fields. On a chemical vapor deposition process of YBa2CU3O7 films deposited on the polycrystalline Ag substrates in high magnetic fields, the microstructure changes drastically from the rectangular large grains with 10 mum in size to the small complex shaped grains. The spiral growth mode is observed for the samples prepared at 0 T but it changes into the island growth mode for that prepared in the presence of a magnetic filed. On a partial-melt process of Bi2Sr2CaCu2O8 tapes in magnetic fields, the homogeneous texture is obtained and it results in the increase of the critical current density. (C) 2003 Elsevier B.V. All rights reserved.

Abstract: The electro-mechanical characteristics of the nickel sheathed powder-in-tube MgB2 mono-core tapes with 10 vol% indium powder were evaluated. No marked change in the stress-strain curve was found by indium addition. On the other hand, the irreversible strain for the tape where a drastic degradation of critical current I-c begins increased from 0.25% to 0.50% by the addition of indium. The indium addition also suppressed the slight increase in I-c with strain. These characteristics of I-c with strain were compared with those reported by other researchers. Scanning electron microscope observations of the longitudinal section of degraded samples revealed that the number of micro-cracks was appreciably smaller in the indium added tapes. (C) 2003 Elsevier B.V. All rights reserved.

Abstract: We have studied the fatigue-damage mechanism of a Nb3Al superconducting composite at room temperature, and the influences of the fatigue damages introduced at room temperature on the critical current at 4.2 K and the residual strength at room temperature. The main (largest) fatigue crack arose first in the clad copper and then extended into the inner core with an increasing number of stress cycles. The cracking of the Nb3Al filaments in the core region occurred at a late stage (around 60-90% of the fatigue life). Once the fracture of the core occurred, it extended very quickly, resulting in a quick reduction in critical current and the residual strength with increasing stress cycles. Such a behaviour was accounted for by the crack growth calculated from the S-N curves (the relation of the maximum stress to the number of stress cycles at failure) combined with the Paris law. The size and distribution of the subcracks along the specimen length, and therefore the reduction in critical current of the region apart from the main crack, were dependent on the maximum stress level. The large subcracks causing fracture of the Nb3Al filaments were formed when the maximum stress was around 300-460 MPa, resulting in large reduction in critical current, but not when the maximum stress was outside such a stress range.

Abstract: The influence of the Ag2O addition on the thermal conductivity K of (Nd-Eu-Gd)Ba2Cu3Oy, melt-textured superconductors with several amounts of NEG-211 phase has been studied. The concentration of added Ag2O is up to 20 wt.%. The distribution of Ag was observed by back electron image. The critical current density evaluated from a magnetization measurement increases with Ag2O at higher magnetic field, which suggests the precipitation of light rare earth (LRE)-rich fine clusters. It was found that the thermal conductivity below T, might be determined by the phonon scattering by the LRE-rich fine clusters, which suppress the enhancement of kappa, and by the improvement of the crystallographic quality with Ag-doping, by which the enhancement is recovered. In almost all of the samples we measured the latter was dominant. The suppression of kappa by the magnetic field H was observed below 110 K. The ratio of kappa(H)/kappa(H = 0) is almost independent of the amount of Ag2O content. (C) 2003 Published by Elsevier B.V.

Abstract: Magnetoelectropolymerization (MEP; electropolymerization under magnetic fields) was applied to the preparation of ferricyanide-doped polypyrrole films, and the redox behavior of ferricyanide ions in the films was investigated. MEP caused a negative shift of the redox potential from 0.2 V to -0.3 V and rendered the electrode reaction irreversible. These findings are discussed in connection with the doping-undoping behavior of the films.

Abstract: Magnetization curves were measured for GdMn2Ge2 single crystals, which show a first-order magnetic transition from a ferrimagnetic state to an antiferromagnetic state at T-1 = 95 K. The field-induced transition from the ferrimagnetic state to a high-field state was observed for both H perpendicular to c and H parallel to c below T-1. The transition field, H-C, in H perpendicular to c goes to zero with increasing temperature to T-1, while that in H parallel to c gradually decreases without falling to zero at T-1. The results were analyzed in terms of a molecular field approximation, in which strong strain dependence of the interlayer Mn-Mn interaction was taken into consideration. The experimental data are well reproduced by the calculated results. The calculations predict that the compound undergoes double magnetic transitions in high magnetic fields for H parallel to c just above T-1, which was confirmed by the measurements.

Abstract: Transport characteristics of Bi-2212 wire in flux-flow state were experimentally investigated under a cryocooled condition in high magnetic fields up to 14 T at various temperatures. The heat balance affected the thermal stability of oxide superconductors, and the oxide superconductor with large current capacity and large n value quenched at the current that was smaller than its critical. current.

Abstract: Superconducting magnets wound with conventional Cu/Nb3Sn are designed considering a stress design criterion of 150 MPa. If the highly strengthened CuNb/Nb3Sn wire is used instead of the conventional CuNb/Nb3Sn wire, the stress design criterion of 250 MPa is applicable. Furthermore, the high strength enables us to make the Nb3Sn superconducting coil using a react and wind method. In order to confirm the stress design criterion of 250 MPa in a CuNb/Nb3Sn coil fabricated by a react and wind method, stress-strain and quench characteristics of the coil were investigated under high electromagnetic stress. The hoop stress of 279 MPa was applied and the measured strain was 0.34%. The quench currents were 50-60% of the critical current for the short sample, and their relevant deterioration of the quench current strongly influenced the large hoop stress. It was confirmed that the design criterion of 250 MPa is adequate for the CuNb/Nb3Sn superconducting coil using the react and wind method.

Abstract: In order to realize a react and wind (R&W) method for Nb3Sn wires, the influences of a bending load at room temperature are investigated. Usually, the superconducting wires undergo bending loads at room temperature repeatedly during winding and insulation processes. We define these bending loads as �pre-bending� treatments. We applied the pre-bending strain of 0 and 0.5% to the highly strengthened CuNb/(Nb, Ti)(3)Sn wires, and measured the stress/strain properties and critical currents. The improvements of stress dependence of normalized critical current and the increase of the maximum critical current by the pre-bending treatments were found. The model based on the distribution of the local tensile strain as a bending strain describes the experimental results well without the increase of the maximum critical current. When the pre-bending strain was applied, the calculated results indicate that the mechanical properties are improved due to the local work hardening, and hence the stress dependence of I-c increases.

Abstract: The magnetic properties of the compound (CePd3)(8)Ge have been studied by means of neutron diffraction and specific heat measurement at ambient pressure and also of measurements of susceptibility and electrical resistivity under hydrostatic pressure. The magnetic modulation vector, q, of the antiferromagnetic phase is 001 and the spin polarization is parallel to q. With increasing the applied pressure up to 6 GPa, the Neel temperature keeps increasing, which indicates a strongly localized nature of the 4f-electrons of the compound.