[en] Nanosystems and strongly correlated systems can possess a more complicated internal Lie-group dynamics in comparison with the Lie-group dynamics of Bose and Fermi systems described by the Heisenberg algebra and superalgebra, respectively. In order to investigate properties of such quantum systems, we represent operators of quantum systems by differential operators over a commutative algebra of regular functionals and develop a new diagram technique on the basis of the expansion of the generating functional for the temperature Green functions. The differential representation makes it possible to generalize functional equations and the diagram technique for the case of quantum systems on topologically nontrivial manifolds by the substitution of the generating functional on a sheaf of function rings on a nontrivial manifold for the generating functional of a constant sheaf of functions. Nontrivial cohomologies of the manifold, on which the quantum system is acted, lead to the existence of additional excitations. We consider the self-consistent-field approximation and the approximation of effective Green functions and interactions. Poles of the matrix of effective interactions and Green functions determine quasi-particle excitations of the quantum system. For special cases of models the diagram expansion is simplified. In particular, if the internal dynamics is determined by the Heisenberg algebra (superalgebra), the diagram expansion reduces to Feynman's diagrams for Bose (Fermi) quantum systems. We consider the reduction of the developed diagram technique and excitations for the case of the spin system with an uniaxial anisotropy

[en] Landau-Lifshitz equations and spin wave damping are derived from first principles by the spin operator diagram technique for the Heisenberg model with magnetic dipole and exchange interactions. It is found that spin excitations, which are determined by poles of effective Green functions, are given by solutions of the linearized pseudodifferential Landau-Lifshitz equations and the equation for the magnetostatic potential. For a normal magnetized ferromagnetic film the spin wave damping has been calculated in the one-loop approximation for a diagram expansion of the Green functions at low temperature. In the framework of the Heisenberg model the magnetic dipole interaction makes a major contribution to the long-wavelength spin wave relaxation in comparison with the exchange interaction. It is found that the damping decreases with increasing film thickness and applied magnetic field and increases directly proportionally to the temperature. For modes of high orders the damping is higher than for the first spin wave mode

[en] We have calculated the exchange interaction between electrons in the accumulation electron layer in the semiconductor near the interface and electrons in the ferromagnet in the ferromagnet/semiconductor heterostructure. It is found that the exchange interaction forms the potential barrier for spin-polarized electrons. The barrier height strongly depends on the difference of chemical potentials between the semiconductor and the ferromagnet. The maximum of the potential barrier height on the temperature dependence is due to the existence of localized electron states in the accumulation layer. In the framework of the developed theoretical model, the injection magnetoresistance effect observed in semiconductor/granular film heterostructures with ferromagnetic metal nanoparticles is explained. A spin filter on the base of granular film/semiconductor/granular film heterostructures operated at room temperature is proposed

[en] The light-induced giant injection magnetoresistance in SiO₂(Co)/GaAs heterostructures, where the SiO₂(Co) structure is the granular SiO₂ film with Co nanoparticles, has been studied. It is found that the photocurrent are accompanied by relaxation oscillations caused by the Coulomb influence and transitions between the photocurrent and electrons on the highest level in the interface quantum well. The light-induced magnetoresistance reaches its maximum value in the avalanche onset region and has the local minimum at the higher voltage. The local minimum is explained by delocalization of the highest level in the interface quantum well and by decrease of the probability of the backscattering process of injected electrons on deeper levels. (paper)

[en] Relaxation losses of magnetic excitations in nanoscale films of Y₃Fe₅O₁₂ (YIG) were studied. The films were obtained by laser molecular-beam epitaxy (LMBE). Ferromagnetic resonance linewidth ΔH was found to increase sharply as the temperature decreased from 300 to 77 K. The observed growth of ΔH is explained by typical relaxation processes caused by the presence of Fe²⁺ ions. This effect is not observed in thick films of YIG grown by liquid-phase epitaxy and containing Pb⁴⁺ ions, and, hence, we have concluded that the presence of acceptor ions in YIG films obtained by LMBE will facilitate decreasing the concentration of Fe²⁺ ions and, a result, diminishing relaxation losses.

[en] We describe the synthesis of nanosized Y₃Fe₅O₁₂ (YIG) films grown by laser-molecular-beam epitaxy on Gd₃Ga₅O₁₂ (GGG) and Nd₃Ga₅O₁₂ (NdGG) substrates with (111) orientation and present the results of ferromagnetic resonance (FMR) and spin-wave propagation studies in these heterostructures. It is found that the magnetic parameters of YIG films grown on NdGG and GGG substrates are considerably different. FMR spectra of YIG/NdGG structures are characterized by a large number of narrow peaks, while FMR spectra of YIG/GGG structures consist of a small number of peaks or one peak. The effective magnetization of YIG films grown on NdGG substrates is less than that of YIG films grown on GGG and is more sensitive to the growth conditions. A lateral inhomogeneity of YIG/NdGG structures is observed in spin-wave propagation experiments. For YIG/NdGG and YIG/GGG structures, the FMR linewidth ΔH of a single peak sharply increases with temperature decrease from 298 to 67 K. The observed increase of ΔH is explained by typical relaxation processes caused by the presence of Fe^2 + ions. From the spin-wave propagation study, it is also found that the relaxation of spin-waves explains only a minor part of the FMR single-peak linewidth in YIG/NdGG structures. On the basis of the obtained results, YIG/GGG/semiconductor- and YIG/NdGG/semiconductor-heterostructures with expected low spin-wave relaxation and desirable effective magnetization profile are proposed. (paper)

[en] Synthesis of nanosized yttrium iron garnet (Y_3Fe_5O_1_2, YIG) films followed by the study of ferromagnetic resonance (FMR) and spin wave propagation in these films is reported. The YIG films were grown on gadolinium gallium garnet substrates by laser molecular beam epitaxy. It has been shown that spin waves propagating in YIG deposited at 700 °C have low damping. At the frequency of 3.29 GHz, the spin-wave damping parameter is less than 3.6 × 10"−"5. Magnetic inhomogeneities of the YIG films give the main contribution to the FMR linewidth. The contribution of the relaxation processes to the FMR linewidth is as low as 1.2%.

[en] We describe synthesis of submicron Y_3Fe_5O_1_2 (YIG) films sputtered on Si substrates and present results of the investigation of ferromagnetic resonance (FMR) and spin waves in YIG/SiO_2/Si structures. It is found that decrease of the annealing time leads to essential reduction of the FMR linewidth ΔH and, consequently, to reduction of relaxation losses of spin waves. Spin-wave propagation in in-plane magnetized YIG/SiO_2/Si structures is studied. We observe the asymmetry of amplitude-frequency characteristics of the Damon-Eshbach spin waves caused by different localizations of spin waves at the free YIG surface and at the YIG/SiO_2 interface. Growth of the generating microwave power leads to spin-wave instability and changes amplitude-frequency characteristics of spin waves

[en] Heterostructures of silicon dioxide films containing cobalt nanoparticles SiO₂(Co) grown on GaAs substrate exhibit at room temperature high values of magnetic field enhancement of photocurrent in the vicinity and above the GaAs bandgap of ∼1.4 eV. For photon energies E above the GaAs bandgap, the photocurrent significantly increases, while the avalanche process is suppressed by the magnetic field, and the current flowing through the heterostructure decreases. The photocurrent is enhanced in the SiO₂(Co 60 at. %)/GaAs heterostructure at the magnetic field H = 1.65 kOe by a factor of about ten for the photon energy E = 1.5 eV. This phenomenon is explained by a model describing electronic transitions in magnetic fields with the spin-dependent recombination process at deep impurity centers in the GaAs interface region

[en] We describe synthesis of submicron Y₃Fe₅O₁₂ (YIG) films sputtered on GaAs-based substrates and present results of the study of ferromagnetic resonance (FMR), spin wave propagation and interaction between spin excitations and 2D electrons in interface layer in YIG/AlO_x/GaAs-heterostructures. It is found that the contribution of the relaxation process to the FMR linewidth is about 3.6%–6.6% of the linewidth . The main contribution to the FMR linewidth of sputtered YIG films is given by a magnetic profile inhomogeneity. Transistor structures with two-dimensional electron gas (2DEG) channels in AlO_x/GaAs interface governed by YIG-film spin excitations are designed. An effective influence of spin excitations on the current flowing through the GaAs 2DEG channel is observed. It is found that the light illumination results in essential changes in the YIG-film FMR spectrum of transistor structures—an increase of the 2DEG current induced by light leads to an inverse effect, which represents essential changes in the FMR spectrum. (paper)