Solid State Phenomena Vol. 215

Abstract: The dependence of free layer coercivity on the angle between easy axis and applied magnetic field was studied on [Ta, (Ni₈₀Fe₂₀)₆₀Cr₄₀]/ Ni₈₀Fe₂₀/Co₉₀Fe₁₀/Cu/Co₉₀Fe₁₀/Mn₇₅Ir₂₅/Ta spin valves with various interlayer coupling. Sharp decrease on the angle was observed for ferromagnetically coupled spin valves. The coercivity was reduced down to tenth of Oersted without any decrease of GMR-effect by forming nearly parallel anisotropy configuration. The angles at which the transition from hysteretic to anhysteretic magnetic reversal takes place are detected by analyses of the angle dependence of coercivity. Interpretation of experimental data is based on Stoner-Wohlfarth coherent rotation approach.

Abstract: Magnetic bioceramics based on hydroxyapatite Ca5(PO4)3OH and particles of the M-type hexagonal (barium or calcium) ferrite (taken in proportions 5, 10, 20, 25, 40 and 50 wt % of M-ferrite) with a high bioactivity and magnetic characteristics providing hyperthermal treatment of oncology diseases has been developed and studied. The phase composition, microstructure, and magnetic properties of the synthesized bioceramics have been determined by using electron diffraction patterns, electron microscope micrograms and Mossbauer spectroscopy. It has been shown that the synthesized biomaterial consists of the biocompatible matrix with the apatite structure into which particles of hexagonal ferrite are incorporated. The Mossbauer spectra for all the samples clearly indicates that the particles of hexagonal ferrite are in the ferromagnetic state and small part of particles in paramagnetic state. The magnetic parameters of the synthesized ceramics are substantially higher than those of the bioglass ceramics modified by iron oxides that have been used in medicine, which suggests good potential and effectiveness of application of the created ceramics for medical purposes. Thus, a new class of magnetic bioceramics combining hydroxyapatite Ca5(PO4)3OH, which exhibits good properties in biocompatibility and bioactivity, with particles of the M-type hexagonal ferrite, which possess high magnetic characteristics, has been created.

Abstract: Magnetic spin valve structures have a great practical interest as sensors of magnetic fields, hard disk read heads and elements of magnetic random access memories (MRAM). Despite the large number of experimental and theoretical work on spin valve structures, the effects of interlayer interactions occurring in these structures, at present time are not fully understood. Introduction

Abstract: The influence of variations of magnetic parameters on the transformations of antiferromagnetic space – modulated structure in BiFeO₃ – like multiferroics is investigated. The specificity of variations of magnetic parameters of different origin namely the magnetic anisotropy, the stiffness, the lattice mismatch between multiferroics film and oriented substrate which can change the conditions of space-modulated structures emergence and the character of space – modulated structures transformations in bulk crystals and thin films is discussed. Threshold parameters of phase transitions between cycloidal structures and homogeneous magnetic states have been found out. It has been shown that plane cycloid can be transformed into conical state during the transition from incommensurate phase into homogeneous phase.

Abstract: On the basis of the micromagnetic simulations we reveal that in the small disk on big disk (d+D) nanostructure it is possible the sustained existence of a single-domain and vortex configurations of magnetization. The presence of the metastable state is possible due to the energy barrier, which is caused by magnetostatic interaction between disks. Switching between states can be performed by the external high frequency excitation. Magnetization switching of the small disk on big disk nanostructure is determined by the interaction of the vortex core in big disk with z-component of the magnetization of small disk.

Abstract: Polycrystalline samples of Bi₂Sn₂O₇ have been synthesized by conventional solid-state reaction method. According to the X-ray powder diffraction research, our sample co-existing of two polymorphs phases: cubic and rhombic, concurrently. The real dielectric permeability Re (ε) monotonic grows versus temperature and the imaginary dielectric permeability Im (ε) nonmonotonic is increased at the heating. There are maxima at Т=450 K on both temperature dependences Im (ε) and Re (ε) reveal. Anomalies in the temperature dependence of electrical resistivity at temperatures are found and to be correlated with the α→ β structural phase transition temperature.