Trends in Magnetism

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Authors: Valentin Yu. Irkhin
Abstract: A review of fundamental works by Shubin and Vonsovsky on the formulation of the polar and s–d(f) exchange models is given. Their ideas are compared with subsequent developments in the theory of magnetism in d- and f-metals and their compounds. Modern approaches including various slave-boson and slave-fermion representations, formation of exotic quasiparticles etc. are discussed. Internal connections between different many-electron models (the Heisenberg, Hubbard, t–J, Anderson Hamiltonians) are presented. Description of anomalous rare-earth and actinide compounds (Kondo lattices, systems with heavy fermions and non-Fermi-liquid behavior) within the framework of the s–d(f) exchange model and related models is considered.
Authors: S.G. Chigarev, E.M. Epshtein, Y.V. Gulyaev, P.E. Zilberman
Abstract: Two channels of the s-d exchange interaction are considered in magnetic junctions. The first channel describes the interaction of transversal spins with the lattice magnetization. The second channel describes the interaction of longitudinal spins with the magnetization. We show that the longitudinal channel leads to a number of significant effects: 1) drastic lowering of the current-instability threshold down to three (or even more) orders of magnitude; 2) creation of sufficiently large distortion of equilibrium due to the current- driven spin injection leading to inversion of populations of the energy spin subbands and laser-like instability in the THz frequency range at room temperature. External magnetic field is likely to tend to additionally lower the instability threshold due to the proximity effect of purely magnetic reorientation phase transition. This effect demonstrates new properties: the giant magnetoresistance (GMR) becomes strongly current-dependent and the exchange switching becomes of very low threshold. We derived some matching condition that should be satisfied to achieve high spin injection level. Some characteristic quantities appeared in the condition, namely, the so called "spin resistances" , where the a number of a layer in the junction. For a three-layer junction ( ), the matching condition is , where the number corresponds to the main functional layer. We investigated also the junctions having variable lateral dimensions of the layers, for example, a ferromagnetic rod contacting with a very thin ferromagnetic film. A large enhancement of the current density can appear near the contact region, leading to the spin injection luminescence.
Authors: L.V. Lutsev, A.I. Stognij, N.N. Novitskii, A.S. Shulenkov
Abstract: The injection magnetoresistance effect in SiO2(Co)/GaAs heterostructures, where SiO2(Co) is a granular SiO2 film containing Co nanoparticles, has been studied. This effect manifests itself in the avalanche breakdown mode and has extremely large values at room temperature due to the spin-dependent potential barrier. We consider application of the IMR effect and SiO2(Co)/GaAs heterostructures in spintronic devices – high sensitive magnetic sensors and field-effect transistors governed by applied magnetic field.
Authors: Martin Gradhand, Dmitry V. Fedorov, Peter Zahn, Ingrid Mertig
Abstract: We present a first-principles study of the extrinsic spin Hall effect due to skew scattering at substitutional defects in noble metals (Cu, Ag, and Au). The dependence of the spin Hall angle on the type of impurity atoms in the host materials is discussed. We perform a detailed analysis based on the consideration of the total angular momentum dependence on scattering phase shifts of the impurity and host atoms.
Authors: A.S. Morozov, L.A. Koroleva, D.M. Zashchirinskii, T.M. Khapaeva, S.F. Marenkin, I.V. Fedorchenko, R.A. Szymczak, B. Krzymanska
Abstract: Based on the Mn-doped chalcopyrites CdGeAs2, ZnGeAs2 and ZnSiAs2, new dilute magnetic semiconductors with the p-type conductivity were produced. Magnetization, electrical resistivity and Hall effect of these compositions were studied. Their temperature dependences of magnetization are similar in form in spite of a complicated character, which is controlled by the concentration and mobility of the charge carriers. Thus, for T < 15 K, these curves are characteristic of superparamagnets and for T > 15 K, of a frustrated ferromagnet. In compounds with Zn these two states are diluted by a spinglass-like state. This specific feature is ascribed to attraction of Mn ions occupying neighboring sites and to competition between the carrier-mediated exchange and superexchange interactions. The Curie temperatures of these compounds are above room temperature. These are the highest Curie temperatures in the AIIBIVCV2:Mn systems.
Authors: E.A. Gan'shina, L.L. Golik, V.I. Kovalev, Z.E. Kun’kova, M.P. Temiryazeva, Y.A. Danilov, O.V. Vikhrova, B.N. Zvonkov, A.D. Rubacheva, P.N. Tcherbak, A.N. Vinogradov
Abstract: Optical and magneto-optical properties of In(Ga)MnAs layers fabricated by laser ablation on GaAs(100) substrates were studied. Spectra of the optical constants and the transversal Kerr effect (TKE) depended substantially on the conditions of layer fabrication and testified to the presence of MnAs inclusions in all the samples. The cross-sectional transmission electron microscopy revealed the presence in the layers of inclusions 10-40 nm in size. At room temperature, a strong resonant band was observed in the TKE spectra of some In(Ga)MnAs layers in the energy range 0.5-2.7 eV. The resonant character of the TKE spectra was explained by excitation of surface plasmons in the MnAs nanoclusters embedded in the semiconductor host.
Authors: I.V. Medvedeva, T. Dyachkova, A. Tyutyunnik, Y. Zaynulin, V. Marchenkov, E. Marchenkova, C.P. Yang, S.S. Chen, K. Bärner
Abstract: Polycrystalline Nd1-xSrxMnO3 was subjected to a thermobaric treatment, that is, a quenching under a high quasihydrostatic pressure of 9 GPa , starting from the temperature 1000 °C. This results in a strong change of the electroresistive and magnetoresistive properties. The changes in the electrical transport might result from the increase of oxygen deficient regions in the boundaries between the nanosized grains.
Authors: N.A. Viglin, V.V. Ustinov, T.N. Pavlov, V.M. Tsvelihovskaya
Abstract: A promising idea to use the transport of spin-polarized conduction electrons in a magnetic hetero-structure in order to invert population of the charge-carrier spin level in one of its layers, aiming at creation of an active environment for the electromagnetic radiation amplification, has been realized in a number of FMС/SC structures in which FMС is a ferromagnetic conductor and SC is a semiconductor. The n-InSb single crystals, featured by a high mobility of charge carriers, narrow ESR line, and anomalously high absolute value of the negative g-factor (g = −52), were used as SC. The following materials were used as FMC playing a role of spin polarizer: (i) ferromagnetic semiconductors EuO0.98Gd0.02O and HgCr2Se4, (ii) Geisler alloys Co2MnSn, Ni2MnSn and Co2MnSb. We have demonstrated that the spin-polarized electrons injection into the n-InSb semiconductor from the above-mentioned ferromagnetic materials results in a generation of the laser-type electromagnetic radiation.

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