Solid State Phenomena Vol. 190

Abstract: New La0.54Ho0.11Sr0.35Mn1-xCuxO3 manganites were obtained by sol-gel method using oxides and acetates and sintered finally in air at 12000 C for 15 h. The samples were studied by X-ray diffraction, magnetic and electric methods. Space group, lattice constants, average size of the crystalline blocks and positions of cations/anions in the unit cell, were determined using the FullProf code. The samples contain only a perovskite phase with an orthorhombic structure (Pnma space group). Small-angle neutron scattering (SANS) measurements were performed on the SANS-1 setup at the FRG-1 reactor of the GKSS Research Centre (Geesthacht, Germany). The sizes of magnetic clusters have been determined at room temperature.

Abstract: We demonstrate that a magnetic tunnel structure irradiated by microwaves can generate a significant voltage signal due to the rectification effect. The measurements were carried out using current-in-plane geometry with a current flowing parallel to the interfaces in the structure. A value of the microwave-induced voltage strongly depends on a bias current and can be driven by a magnetic field. The rectification effect is discussed both in classical terms of nonlinearity of the current-voltage characteristic and using a mechanism that involves the interplay between the spin-polarized current and magnetization dynamics in the magnetic tunnel structure.

Abstract: Longitudinal resistivity in strong parallel magnetic fields up to B = 14 Tesla was measured in Si-MOSFET with a narrow slot (90nm) in the upper metallic gate that allows to apply different gate voltage across the slot and, therefore, to control the electron density n₁ and n₂ in two parts of the sample independently. The experimental scheme allows us to pass through the source-drain channel relatively large DC current (I_DC), while the dynamic resistance was measured using a standard lock-in technique with small AC current. It was shown that the sample resistance is asymmetric with respect to the direction of DC current. The asymmetry increases with increase of magnetic field, DC current, and difference between n₁ and n₂. Results are interpreted in terms of a current-induced spin accumulation or depletion near the slot, as described by a spin drift-diffusion equation. The effect on the sample resistance is due to the positive magnetoresistance of Si-MOSFETs in parallel magnetic fields.

Abstract: The magnetic and electric properties of Fe/Cu/Fe sandwiches deposited on Si were studied in order to improve the efficiency of such a model of spin transistor with a spin-valve. Evaluations of the energy balance and measurements of current dependence on voltage and applied magnetic field confirmed the possibility of amplification increasing in case of additional effect of current on remagnetization.

Abstract: Magnetization and magnetoresistance (MR) studies were carried out on the [Gd/T_n multilayers with different thickness of Gd and Ti layers prepared by magnetron sputtering. The temperature interval of measurements was from 2 to 300 K, for the highest available magnetic field value of 100 kOe. A negative magnetoresistance was observed in all samples. The observed negative MR was analysed by using different magnetoresistance models.

Abstract: We present the first-principles calculations of MPc molecules having the magnetic moment. Some of these molecules contain the magnetic 3d-metal atom (MnPc, FePc, and CoPc), whereas others have the non-magnetic metal atom with an odd number of electrons (CuPc, AgPc, and GaPc). Calculations show that the density functional theory greatly decreases the HOMO-LUMO gap and the spin-splitting energy, comparing with hybrid functional results closely related to the many-electron theory. It is found that the HOMO-LUMO gap of MPc molecules shows moderate changes, while their spin-splitting energy is very sensitive to the localization of spin density and varies very significantly.

Abstract: In this paper, we study the value of the tunnel magnetoresistance (TMR) as a function of the applied voltage in double barrier magnetic tunnel junctions (DMTJs) with the left and right ferromagnetic (FM) layers being pinned and numerically estimate the possible difference of the TMR curves for negative and positive voltages in the homojunctions (equal barriers and electrodes). DMTJs are modeled as two single barrier junctions connected in series with consecutive tunneling (CST). We investigated the asymmetric voltage behavior of the TMR for the CST in the range of a general theoretical model. Significant asymmetries of the experimental curves, which arise due to different annealing regimes, are mostly explained by different heights of the tunnel barriers and asymmetries of spin polarizations in magnetic layers.

Abstract: The experimental results for huge magnetoresistance in polymer/ferromagnet system have been considered. The evidences have been established for the relation of the partially spin-polarized current in the structure and the magnetoresistance events. The model of charge and spin transport of the high-conductive state of wide-band polymer film/ferromagnet heterostructure have been proposed on the base of the experimental data totality.

Abstract: Electromagnetic radiation of 1 - 10 THz range is observed at room temperature in a structure with a point contact between a ferromagnetic rod and a thin ferromagnetic film under electric current of high enough density. The radiation is due to nonequilibrium spin injection between the components of the structure. By estimates, the injection can lead to inverted population of the spin subbands. The radiation power exceeds by orders of magnitude the thermal background (with the Joule heating taking into account) and follows the current without inertia. Efficiency of the oscillator depends strongly on the material used and quantum efficiency may exceed the unity. It means the stimulated radiation processes play an important role.

Abstract: The effect of the atomic disorderorder transformation on remanence, coercivity and magnetic anisotropy energy in CoPt nanoparticles prepared by thermal decomposition and annealed at 400°C for 4 and 16 hours has been studied. The observed remanence and magnetic anisotropy energy enhancement versus annealing time are discussed in the terms of ordering domain formation inside nanoparticles.