Solid State Phenomena Vols. 233-234

Abstract: The present work deals with investigation of features of a magnetization vector of nonlinear precession and elastic displacements close to ferromagnetic resonance in normal magnetized ferrite plate. The system of ordinary differential equations was solved numerically by the Runge-Kutta 7-8 orders method with control of the integration at every step length. The possible excitation of magnetoelastic autooscillations was found out in the paper. Two mechanisms of autooscillations: reorientation and detuning were investigated. The boundaries between the regular and chaotic reorientation autooscillations depending on the magnetic dissipation parameter and magnetoelastic interaction constant were determined.

Abstract: Microwave magnetic induction structure of a surface spin wave propagated in a free ferrite film is calculated. It is found that vector lines of magnetic induction represent vortexes localized near both surface of the ferrite film. The relationship between microwave magnetic induction structure and microwave electric field structure of spin wave are demonstrated.

Abstract: Excitation of hypersound elastic oscillations in the microwave on the magnetization reversal of the normal magnetized ferrite plate is studied in the paper. Characteristic times of the process of development of magnetic and elastic oscillations were revealed. Their relation to the parameters of the magnetic and elastic damping has been revealed.

Abstract: Monolayer composite, multilayer composite-composite and multilayer composite-semiconductor films were investigated. Dependencies of the internal exchange fields on magnetic metal alloy concentration in nanostructured single and multilayer films at room and liquid nitrogen temperatures were obtained. The calculation is made on the basis of the experimental data and the relationship of the exchange interaction and the broadening of the FMR line.

Abstract: To calculate the torque acting on the magnetization vector during the process of 90° pulsed magnetization in real ferrite-garnet films in which, besides in-plane anisotropy, biaxial anisotropy is present, the method based on the analysis of the operating point trajectory is used. Analysis has shown that the shape of the time dependence of the torque T_φ in the time interval, within which the exciting of the magnetization oscillations occurs, is slightly dependent on the pulse front duration. As a result the magnetization oscillations (with a period of T_os ≅ 2 ns) can be observed at the pulse front duration τ_f ≥ 14 ns.

Abstract: In this work we report the study of magnetic relaxation process presented in the bimetallic Co/Au nanoparticles prepared utilizing the reverse micelle method. Structural analysis of the system using synchrotron X-ray diffraction and transmission electron microscopy documented individual nanocrystalline particles of average size about 7 nm. Magnetic properties of the particles were examined by ac magnetic susceptibility measurements at temperature range 2 – 300 K at different frequencies of magnetic field. The relaxation process was revealed at temperature about 6 K. Application of several theoretical models on experimental data of magnetic susceptibility confirmed strong inter-particle interactions and novel superspin glass state in the nanoparticle system at low temperatures.

Abstract: Magnetoresistive effect and electrotransport properties of Ni_х(MgO)_100-х (x: 21-48 at.%) granular composites have been investigated. It is found that prepercolated composites (x < 24 at.%) do not exhibit magnetoresistive properties. After percolation threshold (x: 27-29 at.%) the composites exhibit isotropic negative magnetoresistance (-0,2 %) which has not tunneling nature. Also weak localization is realized in these samples at temperatures below 100 K. At high metal concentration (32 at.% < x) the composites exhibit anisotropic magnetoresistance.

Abstract: The research of magneto-optical properties has been conducted for the “Nanocomposite-bismuth telluride” (Co₄₀Fe₄₀B₂₀)_33.9(SiO₂)_66.1/[Te₃Bi₂] multilayer system at various thicknesses of each layer type. We report an enormous enhancement of magneto-optical (MO) response in this system. Besides, a good correlation between thickness dependences of transversal Kerr effect (TKE) and magneto-transport properties has been established. Such correlation was related to peculiarities of the interface forming process at the ferromagnetic (FM) granule boundaries. Moreover, this amplification of magneto-optical response is largest among the other spacer layers, such as Si, Cu, and C, therefore a comparison between them has been plotted.

Abstract: Ferromagnetic (FM) FeCo is investigated in exchange bias systems. The ferromagnetic layer is grown on a FeMn antiferromagnetic (AFM) layer. Partial superficial oxidation of FeCo is observed. The standard field cooling procedure results in a large room temperature exchange bias effect. However, the training effect observed when the hysteresis loops are repeated does not have a saturating trend. This behavior is related to the evolution of pinned moments at the FM/AFM interface. X-ray circular magnetic dichroism technique is used to clarify this mechanism.

Abstract: Spherical nickel nanoparticles were prepared by the electrical explosion of wire. The as-prepared nanoparticles were modified immediately after fabrication at room temperature in order to provide tunable surface properties with focus on the development of composites filled with nanoparticles. Following liquid modificators were used: hexane, toluene and the solution of polystyrene in toluene. In one case the surface modification by carbon was made in gas phase as a result of hydrocarbon injection. The average size of the nanoparticles was about 50 nm and unit cell parameters were close to 0.351 nm. Detailed characterization was done by X-ray diffraction, transmission electron microscopy, and magnetization measurements. Sphericity was also checked using microwave resonant absorption.