Abstract: We study the precession frequency and effective damping of patterned permalloy thin films of different geometry using integrated
inductive test structures. The test structures consist of coplanar wave guides fabricated onto patterned permalloy stripes of different
geometry. The width, length and position of the permalloy stripe with respect to the center conductor of the wave guide are varied. The
precession frequency and effective damping of the different devices is derived by inductive measurements in time and frequency domain
in in-plane magnetic fields. While the precession frequencies do not reveal a significant dependence on the sample geometry we find a
decrease of the measured damping with increasing width of the permalloy centered underneath the center conductor of the coplanar
wave guide. We attribute this effect to an additional damping contribution due to inhomogeneous line broadening at the edges of the
permalloy stripes which does not contribute to the inductive signal provided the permalloy stripe is wider than the center conductor.
Consequences for inductive determination of the effective damping using such integrated reference samples are discussed.
Index Terms—Ferromagnetic resonance, Gilbert damping, magnetic films, magnetic materials, magnetic variables measurements,
nanostructured materials, permalloy, PIMM, thin films, VNA-FMR.
Abstract: The preparation of ZnSn-substituted barium ferrite films by sputtering deposition was studied. The as-sputtered films were amorphous, and annealing at a minimum of 750 1C was required to crystallize the films, based on the X-ray diffraction analysis and the magnetic measurements. Scanning electron microscopy combined with energy-dispersive X-ray spectroscopic microanalysis confirmed that the films were single phase with the composition BaZnxSnxFe122xO19, x¼0.20.3, and their thicknesses were 0.4–1.0 mm when annealed at 750–900 1C. Atomic and magnetic force microscopy studies showed no significant grain growth upon annealing and that the films consisted of single-domain grains forming interaction-cluster-type domains. The natural ferromagnetic resonance frequency was determined at around 4 GHz, together with substantial magnetic losses that make these films promising candidates for microwave absorbers.
Abstract: The magnetic properties of FeTb rf-sputtered thin films have been investigated. While the as-prepared films are mainly amorphous, a successive annealing process caused the development of successive crystal phases.We observed the emergence of a variety of different domain structures, as the system crystal fraction evolves. The hysteretic behavior is shown to change as the internal stresses are released
by annealing.
Abstract: The giant magnetostriction observed in rare-earth transition-metal compounds such as Terfenol-D
(Tb0.3Dy0.7Fe2) is commonly associated with the huge anisotropy of the 4f electron cloud. We report here the
experimental observation of this phenomenon at the atomic scale, in amorphous matter. By using extended
x-ray absorption fine structure spectroscopy in a differential mode, the bond strains resulting from the coupling
between the anisotropic shape of the Tb 4f charge density and the environment crystalline electric field are
measured. In a-TbFe2 we measure Fe-Fe and Fe-Tb bond contractions equal to 6(1)x10−4 Å and of 9(2)x10−4 Å, respectively. These are the smallest atomic displacements ever detected in amorphous matter.
Abstract: Thick coatings of CoTi-substituted Ba hexaferrite with the
nominal composition BaCoTiFe10O19 were prepared using atmospheric
plasma-spraying technology. The coatings were prepared
from prereacted powders of the desired composition. The
as-deposited coatings showed a high degree of crystallinity. A
detailed investigation of the coatings’ phase compositions was
conducted with micro-Raman spectroscopy and energy-dispersive
X-ray spectroscopy. Two magnetic ferrite phases, CoTisubstituted
Ba hexaferrite and Co ferrite, were identified in the
coatings. An X-ray powder-diffraction analysis and a quantitative
structural analysis based on Rietveld refinement showed that
the mass ratio of the two phases and their chemical composition
varied with respect to the spraying parameters. Consequently,
the static and microwave magnetic properties of the as-sprayed
coatings also varied. We were able to explain the formation
of the two ferrite phases based on the interplay between the
partial melting of the feedstock powder and the recrystallization
kinetics.
Notes: This work was carried out in the frame of the EU6, MATERA ERA-NET, 4302-31/
2006/26, ABSOFILM project with the financial support of the Ministry for Higher Education,
Science and Technology of the Republic of Slovenia, Tekes, Finnish Funding
Agency of Technology and Innovation, the Ministry of Innovation, Science, Research and
Technology of the State of North Rhine-Westphalia of Germany, and INRIM.
wAuthor to whom correspondence should be addressed. e-mail: darja.lisjak@ijs.si
Abstract: The influence of a rotating magnetic field on disk-shaped twinned Ni-Mn-Ga single crystals is studied
theoretically and experimentally. A magnetoelastic model of ferromagnetic martensite is used for the comprehension
of experimental results. The model considers the magnetic field influence on each twin component in
terms of the magnetically induced mechanical stress magnetostress. The angular dependence of magnetostress
and the correspondence between the directions of the magnetic field and magnetization vector are
obtained. The magnetically induced transformation of twin structure of the specimen is observed experimentally
in a Ni52.0Mn24.4Ga23.6 single-crystalline disk by magnetic measurements performed in a two-dimensional
vibrating sample magnetometer. The threshold character of the transformation process is stated. The threshold
angles between the 100 crystallographic direction and the directions of magnetic field and magnetic vector of
the transformed twin component were measured for the different magnetic field values. The comparison of
experimental values with the theoretical ones points to the comparatively low value of the magnetic anisotropy
constant 50 kJ m−3. The obtained results disclose the possibility of obtaining large magnetically induced
strains in ferromagnetic-shape memory alloys with reduced magnetocrystalline anisotropy.
Abstract: In this research, Ba-hexaferrite coatings for electromagnetic wave absorption applications were deposited by thermal spraying. A suitable powder feedstock was manufactured by blending a BaCO3+Fe2O3 mixture, which was then agglomerated by spray-drying. The agglomerates were processed by air plasma spraying (APS) without any further treatment or were heat-treated and reactively-sintered to stoichiometric Bahexaferrite prior to spraying. As-sprayed coatings were analyzed by Raman spectroscopy and X-ray diffraction (XRD). Whereas the deposition of untreated agglomerates did not result in adequate amounts of crystalline Ba-hexaferrite in the coatings, the APS processing of reactively-sintered agglomerates led to a high content of Ba-hexaferrite and similar magnetic properties to those of Ba-hexaferrite bulk materials.
Abstract: Vortex oscillations induced by dc currents (Idc) through a metallic nanocontact subject to in-plane magnetic fields (Hext) are studied by measuring voltage power spectra. Two oscillations modes exist: at large Idc the oscillation frequency (fosc) is substantially insensitive to Hext, whereas at low Idc, fosc decreases with Hext increasing. At intermediate Idc the two modes coexist. This behavior is ascribed to the magnetic states of the device ferromagnetic layers: in the first mode vortices are formed in both layers while in the second mode one layer is in a vortex state while the other is in a quasiuniform state.
Abstract: The phase transitions of off-stoichiometry single crystals of Ni2MnGa, observed by varying the sample temperature and the applied stress, are shown to be strongly influenced by the presence of a magnetic field. The single crystals present a first order phase transition from a paramagnetic-austenite to a ferromagnetic-martensite: stress, temperature and field may cooperate to induce the phase transition when a proper choice of experimental procedures is made. Strains of the order of several percent are observed and connected with super-plastic and super-elastic phenomena. Such phenomena are strongly affected by a unidirectional magnetic field, which produces effects similar to an applied stress. Entropy changes due to the application of magnetic field and stress are analyzed in the framework of the Clausius-Clapeyron equation.
Abstract: Iron oxide nanoparticles with diameter around 10 nm were produced and injected in 60 m thick
anodic alumina membranes with pore diameters of 20 and 100 nm. The structure, magnetic
properties, and the ferromagnetic resonance frequency of the nanoparticles before and after injection
into the columnar arrays were measured as a function of the out-of-plane applied field. The effect
of dipolar interactions and clustering mechanisms of the injected nanoparticles on the static and
radio frequency magnetic response is discussed.
