Solid State Phenomena Vols. 168-169

Abstract: The GaAs doped with donors manifests long times of spin relaxation, while in the case of acceptors (or magnetic impurities) spin relaxation rate increases markedly, in accordance with theoretical predictions. From the practical point of view, this situation is unfavorable, since the devices based on spin degrees of freedom require long times of the spin memory. Therefore semiconductors such as p-GaAs were not considered as promising materials for spintronics. In the present work this conclusion is refuted by means of investigation of the spin dynamics of electrons in epitaxial layers of gallium arsenide doped with Mn impurities. In spite of the expectations, we have discovered the suppression of the spin relaxation of electrons in GaAs:Mn by two orders of magnitude. This effect is a consequence of compensation of the hole and manganese effective magnetic fields due to the antiferromagnetic interaction. The analogous results obtained for the case of GaAs quantum well doped with Mn [R. C. Myers, et al., Nature Materials 7, 203 (2008)] were interpreted as the result of the spin precession of magnetic acceptors rather than electrons. Through separate measurements of g-factor by means of time resolved spectroscopy it has been proved that long times of spin relaxation in p-GaAs:Mn relate to electrons and not to magnetic acceptors. The oscillation frequency of the angle of Kerr rotation depends linearly on the magnetic field and complies with g=0.46±0.02, i.e. the electronic g-factor.

Abstract: Circularly polarized electroluminescence from light-emitting diodes based on InGaAs/GaAs heterostructures with adjacent ferromagnetic delta-doped layer has been investigated. It was found that delta-layer placed near (at 2-10 nm) the quantum well (QW) causes circular polarization of its electroluminescence due to an s,p-d exchange interaction between holes in the quantum well and Mn ions in the delta-layer. The dependence of circular polarization degree on main technology parameters is discussed.

Abstract: The work is devoted to the discussion of magnetic dynamics features in mesoscopic magnetic structures under the action of spin transport and spin-torque transfer in the nanopillar structures. Tunneling magnetic structure consisting of autoemission cathode and patterned magnetic anode is considered. Main bifurcation changes in the states of a dynamical system, that models mesoscopic structure, are discussed for varied spin polarized current and an external magnetic field.

Abstract: The idea of establishing coherent relaxation in an assembly of magnetic moments by placing it in a passive resonator [1, 2] is applied to the case of single-domain ferromagnetic nanoparticles. The magnetodynamics of a particle is governed by the Landau-Lifshitz equation modified by adding the resonator feedback field. The particle uniaxial magnetic anisotropy and the interparticle dipole-dipole interactions are taken into account.

Abstract: FMR and SWR spectra of exchange-coupled structures NiFe/Ag/NiFe have been investigated. We revealed that the optical satellites of the exchange spin-wave modes are characterized not by the standard Kittel-dependence but rather by their own resonance field dependence on the mode number: Hropt(n)~n5/2.

Abstract: For the first time characteristic modification of a spectrum of the exchange spin waves, caused by the first stop-band at a wave vector kb=π/(d1+d2) the magnon crystal formed by one-dimensional modulation of the exchange or magnetization has been found by the spin-wave resonance (SWR) technique in multilayer structures “ferromagnet/ferromagnet” with N(d1+d2) thickness. It is shown that at transformation of a multilayer film after thermal annealing in a film of a single-phase alloy the given modification of a spectrum disappears.

Abstract: We investigate the conditions of capturing into resonance and exciting nonlinear ferromagnetic resonance in a ferromagnetic film with the anisotropic easy plane, as well as autoresonance excitation of nonlinear oscillations of the domain wall in uniaxial ferromagnets. The investigations demonstrate that in easy-plane ferromagnets with a narrow resonance line nonlinear oscillations of magnetization in the autoresonance mode can be generated. This autoresonance takes place if the resonance field grows slowly and pumping frequency is the constant which is equal to the frequency of linear resonance. It has been established that effectively exciting nonlinear oscillations of the domain wall in uniaxial ferromagnets and controlling the wall dynamics by low-amplitude alternating fields with the slow variation of the planar field in the autophasing mode are possible in the case of weak dissipation.

Abstract: The paper investigates the autoresonance parametric method of excitation of a magnetization breather in a uniaxial ferromagnet by an external alternating magnetic field. The breather excitation threshold has been determined, as well as its dependence on the material quality factor.

Abstract: Waves in the superlattice (SL) contained inhomogeneities with anisotropic correlation properties are considered. The anisotropy of the correlations is characterized by the parameter , where and are the correlation wave numbers along the axis of the SL and in the plane of its layers, respectively ( and are the correlation radii). Dependencies of both the dynamic susceptibility and density of states at the continuous transition from the isotropic three-dimensional inhomogeneities ( ) to the one-dimensional ones ( ) have been obtained.

Abstract: The interaction of spin, ferroelectric and elastic subsystems is investigated in antisegnetoantiferromagnetic crystal depending on the magnetic and electric fields, and also on an external mechanical pressure. It is shown that the magnitude of the magnetoelectric interaction increases with the rise of an external magnetic field and decreases with increasing external electric field.