Solid State Phenomena Vol. 190

Abstract: Using the method of angular dependence of ferromagnetic resonance field the magnetic properties of Si/SiO₂/Cu/Co/FeMn/Cu and Si/SiO₂/Cu/Co/Cu/FeMn/Cu structures were investigated. The layer deposition was carried out by magnetron sputtering in absence of an external magnetic field. It was established that thermal annealing with further cooling down in presence of a magnetic field can generate an exchange bias at anneal temperature significantly below the bulk antiferromagnetic Néel temperature. It was also shown that a thin interlayer between ferromagnetic and antiferromagnetic layers reduces the exchange bias effect at low anneal temperatures, however, makes this effect more stable at high annealing temperatures.

Abstract: Transport phenomena in manganites (ABO₃), and indirectly the transition temperature from metallic to insulator state (T_MI), can be controlled by hole doping and the average ionic size at A positions (). In agreement with Zener theory, the strength of double exchange is determined by the Mn-O length (d_MnO) and Mn-O-Mn angles () of the Mn-O-Mn bonds. We will investigate the influence of substitution of Mn with V on the crystalline structure and transport characteristics in La_0.54Ho_0.11Sr_0.35Mn_1-xV_xO₃ manganites. The samples were prepared by sol-gel method to improve the purity and homogeneity of the samples. By XRD it was established that the samples contain only ABO₃ perovskite phases, except the samples with x0.1. The resistance of the samples vs temperature was determined by four probes method. The specific magnetization was obtained by using a Foner type magnetometer, working at 1.4 T, between 77 and 400 K.

Abstract: The electroluminescence properties of ferromagnetic GaMnSb/GaAs diodes have been investigated. It has been found that diodes properties are significantly dependent on GaMnSb layer electrical properties. The intensity of electroluminescence of the diode with semiconductor GaMnSb contact is relatively low, that is due to a high potential barrier at the interface. In case of metallic GaMnSb/GaAs contact high hole injection efficiency provides relatively high electroluminescence intensity. Investigated light-emitting diodes can be prospective for investigation of spin injection effects.

Abstract: By measuring the angular dependence of ferromagnetic resonance field at room and low temperatures, it is demonstrated that the magnitude of magnetic field applied during magnetron deposition of Ta/F/AF/Ta structures, where F=Co, NiFe and AF=FeMn and IrMn, influences the uniaxial and unidirectional anisotropy, magnetization and the exchange bias blocking temperature. The deposition field effects on the bilayer structure are compared with the effects on a similar structure, but without antiferromagnetic layer. The exchange bias blocking temperature of investigated structures is found to be significantly lower than the Néel temperature of a bulk antiferromagnet. The origin of the observed effects is shortly discussed.

Abstract: We report the magnetic properties of Eu_xCa_1-xB₆ single crystals (0.756x1) studied in the wide range of temperatures (1.8-300 K) and magnetic fields (up to 50 kOe). It was found that low field magnetic susceptibility χ (T) follows the Curie-Weiss law χ~(T-Θ_p)^-1 at high temperatures for all the concentrations studied. The effective magnetic moment of the Eu²⁺ ion estimated from the data diminishes from the free ion value μ_eff7.93μ_B (μ_B - Bohr magneton) for x=1 to μ_eff7.3μ_B for x=0.756. A universal behavior of magnetic susceptibility χ~(T-Θ)^-α (α=1.5) is detected close to the Curie temperature T_C in the paramagnetic state at both metallic (x>x_C~0.8) and dielectric (xC.

Abstract: We calculate the TMR of a quantum nanowire with circle cross section consisting of two ferromagnetic electrodes separated by an insulator based on the nearly-free-electron approximation. The dependence of TMR to applied voltage by different cross-sections of nanowire and different electron effective mass of nanowire are studied theoretically.

Abstract: t is reported about fabrication by laser deposition in a gaseous environment of epitaxial layers of ferromagnetic semiconductors GaMnSb and InMnSb. Investigations of x-ray diffraction and Raman scattering showed reasonably good crystal quality of GaMnSb and InMnSb layers. Magnetic properties were investigated by magneto-optical transversal Kerr effect and Hall effect. It is established, that GaMnSb layers are ferromagnetic at room temperature. In contrast, InMnSb samples demonstrate the ferromagnetic properties only at low temperatures (< 70 K).

Abstract: Energy difference between the ferromagnetic and antiferromagnetic collinear orderings has been calculated for the uniform and dimer Mn-pair geometries in order to find the ground state distribution of the Mn atoms in InSb (As) hosts. We find the preference of the dimer ferromagnetic configuration of Mn dopants and an importance of optimizing the atomic site positions. The frequency-dependent optical and magneto-optical properties, namely the reflectivity, the electron energy loss spectra, on-and off-diagonal conductivity tensor and the polar Kerr effect, are calculated for comparison with available experimental data. Our calculated MO resonance in In_1-xMn_xSb (x=1.56%) are found to be in good agreement with corresponding experimental MO spectra. The origin of the large Kerr rotation is discussed.

Abstract: Transport of electronic spins in low-dimensional and nanoscale systems is the subject of thenovel and quickly developing eld of spintronics. The possibility of coherent spin manipulationrepresents an ultimate goal of this eld. Typically, spin transport is strongly aected by couplingof spin and orbital degrees of freedom. The inuence of the spin orbit interaction is twofold.The momentum relaxation due to the scattering of carriers, inevitably leads to spin relaxationand destroys the spin coherence. On the other hand, the controlled orbital motion of carrierscan result in a coherent motion of their spins. Thus, the spin orbit coupling is envisaged as apossible tool for spin controling in electronic devices. In particular, it is possible to generatespin polarization and spin currents by applying electric eld, the phenomenon known as thespin-Hall eect (SHE) [1- 3]. The eect is manifested in the form of a spin current directedperpendicular to the normal current, which takes place in an electric eld.