Solid State Phenomena Vol. 190

Abstract: FMR and SWR spectra of exchange-coupled structures NiFe/Cu/NiFe, NiFe/Ag/NiFe and NiFe/DyCo/NiFe have been investigated. We revealed that the optical satellites of the exchange spin-wave modes are characterized not by the standard Kittle-dependence but by their own resonance field dependence on the mode number: H_r^opt(n) ~ n^5/2.

Abstract: Exchange bias and coercivity of the hysteresis loop of a low-coercive layer in magnetic three-layered structure prepared by chemical deposition are studied. It is established that the coercive force in the films obtained nonmonotonically changed with the low-coercive layer thickness. The specificity of magnetization reversal of exchange-biased layers is analyzed.

Abstract: Magnetic properties of (Co₄₀Fe₄₀B₂₀)_X(SiO₂)_100-X nanogranular composite films, [(Co₄₀Fe₄₀B₂₀)_X(SiO₂)_100-X /a-Si:_n multilayer films and layered (Co₄₀Fe₄₀B₂₀)_X(SiO₂)_100-X films with X ranging from 30 to 80 have been characterized by means of magnetic measurements and ferromagnetic resonance. Layer thickness was varied between 1.3 and 6 nm. Thermal decrease of (Co₄₀Fe₄₀B₂₀)_X(SiO₂)_100-X composite magnetization follows the T^3/2 law. The spectrum of standing spin-wave has been detected in the perpendicular experiment configuration for films with the metal phase content above 48 vol. %. It is found that the H_r(n²) dependencies are non-linear. Such behavior is probably caused by the fluctuations of magnetic parameters (the magnetization and the ferromagnetic exchange coupling) in nanocomposite films. A comparison between the magnetic properties of (Co₄₀Fe₄₀B₂₀)_X(SiO₂)_100-X granular films and [(Co₄₀Fe₄₀B₂₀)_X(SiO₂)_100-X /a-Si:_n multilayer films was carried out.

Abstract: Powders of Ñî-Ð alloy with ultradispersed corundum (Al₂O₃) and detonation nanodiamond (DND) precipitates were synthesized by chemical reduction. The products were characterized by X-ray diffraction and scanning electronic microscopy. The shape of the particles was spherical and they were ferromagnetic. Magnetization dependence on field in applied fields of up to 40 kOe and magnetization dependence on temperature in the temperature range from 2 to 300 K were measured. Influence of precipitates on magnetic properties was studied.

Abstract: In the present work, we have studied the structural, magnetic and magnetoresistive properties of Co_x(SiO₂)_100-x and Co_x(Al₂O₃)_100-x composite thin films, obtained by magnetron co-sputtering of metallic and insulator targets. It was shown by transmission electron microscopy and by temperature and field dependences of the magnetization that the films have a fine granular structure. For a wide range of compositions an adequate description was possible in frame of the model of homogeneous non-interacting superparamagnetic hexagonal lattice Co particles. Magnetoresistive sensor prototypes were designed on the base of an optimized magnetoresistive Co₅₀(Al₂O₃)₅₀ composite films

Abstract: Conditions of coexistence of Fe/Cr/Fe film states with parallel and antiparallel Fe layer magnetisations orientation are established. The transition from antiparallel to parallel orientation in external magnetic field is caused with Cr layer spin density wave phase change when wave node in the centre of Cr layer is substituted with wave antinode. The coexistence of these two states means that Fe/Cr/Fe film ferromagnetic state created with external magnetic field retains after the switching this field off. This phenomenon will manifest itself in the fact that magnetisation curve of initially antiferromagnetic Fe/Cr/Fe film will go outside the hysteresis loop of it's remagnetisation in ferromagnetic state created by external field.

Abstract: Elastic properties of rare-earth cobaltites RBaCo₄O₇ (R = Y, Er - Lu) are studied in the temperature range (4.2 - 300) K. Significant softening of Youngs modulus for Lu-and Yb-cobaltites is found at temperature decrease, showing an instability of the crystal structure and accompanying by a reverse jump at the structural phase transition. Softening and jump at phase transition decrease more than by the order of value, while the transition temperature T_s and hysteresis dT_s enlarge from Lu-to Tm-and Er-compounds. Smooth and weak elastic anomaly at the magnetic phase transition is found resulting from low dimension and frustration of exchange interactions in the Co subsystem in most of the rare-earth cobaltites studied.

Abstract: The quantitative analysis of static ferromagnetic correlations in nanocrystalline films Fe₇₈Zr₁₀N₁₂ was performed by two methods: the correlation magnetometry technique and magnetic force microscopy. The data, obtained by both methods, prove to be in good agreement.

Abstract: At the present time two models can more or less describe the magnetic properties ofNi4Mo12. The rst one is based on the assumption of essential role of non-Heisenberg exchangeinteractions. The key feature of the second model is the symmetry breaking of exchange inter-actions. The present work is focused on the forecasting power of these spin models. Mechanismresponsible for non-Heisenberg exchange interactions is the same as mechanism resulting in in-teraction of spin chirality with external magnetic eld. An additional level splitting in magnetic eld can be observed in this case. The symmetry breaking of exchange interactions inevitablyleads to nonzero toroidal moment and related to it magnetoelectric phenomena.

Abstract: We study the effect of magnetic doping on appearance of ferromagnetic (FM) order on the surface of a three-dimensional topological insulator. Assuming the exchange coupling of the Dirac fermions with the dilute magnetic ions, we find that the system under consideration is unstable with respect to a spontaneous uniform magnetization along the out-of-plane direction. The appearance of the magnetization is accompanied by opening of a gap in the spectrum of surface states. In the framework of a mean-field approach, we analyze the possibility of the FM order on the magnetically doped surface of topological insulator at different temperatures and positions of the chemical potential.