Solid State Phenomena Vols. 233-234

Abstract: The Influence of the ferromagnetic (FM) and antiferromagnetic (AFM) layers position and of the thickness of antiferromagnetic (AFM) layer on magnetic properties of FM/AFM bilayer structures was studied. Angular dependences of the coercive force and exchange bias field were analyzed for NiFe/IrMn bilayer structures with different thickness of AFM layer. In some samples we observed the maximum values of the exchange bias field in the directions different from the magnetic easy axis.

Abstract: Magnetization dynamics in a three-layered nanopillar Co/Cu/Co structure with one fixed and one free layer driven by external magnetic field and spin-polarized electric current was investigated using methods of the theory of bifurcations. Mathematical model is based on the Landau-Lifshits-Gilbert equation with the current term in the Sloncžewski–Berger form. Orientation of applied magnetic field was considered to be parallel to the anisotropy axis. Physical model included the magnetocrystalline anisotropy field and the demagnetizing field. Because of small size of the structure, the space dependence of magnetization, as usually, was not taken into account. The resulting system of equations has the form of the nonlinear dynamical system with the polynomial right sides. Mathematical simulation of magnetization dynamics for several typical values of field and current was performed. The numerical experiments revealed the features of switching process in more detail and permitted to find new regimes of magnetization dynamics, such as incomplete and accidental switching.

Abstract: The solitary deflection waves accompany moving antiferromagnetic vortices in the domain wall of yttrium orthoferrite. These waves allow to investigate generation and nonlinear dynamics of these vortices on the moving domain wall with the help of two-and three-fold digital high speed photography. As the domain walls and the antiferromagnetic vortices dynamics is quasi-relativistic with the limiting velocity c=20 km/s, which is equal to the spin-wave velocity. The dynamics of solitary deflection waves can be explained assuming existence of the gyroscopic force. This work is devoted to experimental results on the dynamics of the solitary deflection waves on the domain wall of yttrium orthoferrite.

Abstract: Magnetic state of epitaxial heterostructures La_0.7Sr_0.3MnO₃/LaMnO₃/SrRuO₃ (LSMO/LMO/SRO) was studied by SQUID magnetometer, ferromagnetic resonance (FMR) and polarized neutron reflectometry (PNR) techniques. The fit of PNR and FMR data give us the magnetization of each layer, while the SQUID gives the total magnetization of our structures. The magnetic moment of the LMO layer has the magnetization 4πM_LMO=4.2kGs (2.4 m_B/Mn) at T=140K according to our PNR data fitting.

Abstract: Domain walls in iron garnet films demonstrate magnetoelectric properties that manifest themselves as a displacement induced by inhomogeneous electric field. In this paper the results of the study of electric field induced domain wall dynamics and its dependence on external magnetic field are presented. The measured velocity of the electrically induced domain wall motion increased by an order with the magnetic field applied perpendicular to the domain wall plane. The numerical simulation shows that the observed behaviour of the domain wall can be explained by magnetic field induced modification of its internal micromagnetic structure and enhancement of the electric polarization associated with the wall.

Abstract: The transport, resonance and optical properties of anion-substituted manganese chalcogenides MnSe_1-xTe_x in the 77-300 K temperature range in magnetic fields up to 1T are studied. The magnetoresistance effect with the maximum value in the vicinity of the Neel temperature for the composition x = 0.1 is revealed. EPR data indirectly indicate the type of the current carriers – lattice polarons. The changes in electron structure occurring due to the anionic substitution are studied using the optical methods.

Abstract: We report the giant magnetoimpedance effect in a ferromagnetic metal/insulator/semiconductor (MIS) diode with the Schottky barrier based on the Fe/SiO₂/n-Si structure. It was established that the applied magnetic field strongly influences the impedance of the structure in the temperature range 10—30 K. In this range, there is the pronounced peak in the temperature dependence of the real part of the impedance at frequencies from 10 Hz to 1 MHz. The effect of the magnetic field manifests itself as a shift of the peak of the real part of the impedance. Under the action of a bias voltage of 5 V, the peak of the real part of the impedance similarly shifts toward lower temperatures with and without applied magnetic field.

Abstract: The results of experimental observations at room temperature of anomalous Hall effect associated with existence of a spontaneous spin polarization of conduction electrons in mercury selenide crystals doped with chromium and vanadium in the concentration range from 1·10¹⁸ to 1·10¹⁹ sm^-3 are reported. Comparison of the experimental data together with the previously reported results related to crystals with iron, cobalt and nickel impurities shows that the relative contribution to the anomalous Hall effect is maximal for vanadium impurity (≈ 13%) and minimal for iron impurity (≈ 5%). Also, transverse magnetoresistance with a characteristic dependence on the magnetic field strength, on which an unusual hysteresis in the field dependence was observed, was found in investigated crystals at room temperature. Theoretical interpretation of the observed effects is developed based on the concepts of thermodynamic nature of anomalous galvanomagnetic phenomena in electron systems with spontaneous spin polarization.

Abstract: The influence of bias current on the second harmonic in the nonlinear magnetoimpedance in an amorphous microwire with a helical anisotropy is studied theoretically. The voltage response of the microwire is found in the framework of a rotational model. It is shown that the application of the bias current leads to the asymmetry in the field dependence of second harmonic. The second harmonic amplitude is analyzed as a function of the external field, current amplitude and the value of the bias current. The conditions of maximum field sensitivity of the second harmonic are found.

Abstract: New {[({[(Co₄₁Fe₃₉B₂₀)_X(SiO₂)_100X]/[(Co₄₁Fe₃₉B₂₀)_X(SiO₂)_100х+O₂]}₁₇₈ and {[(Co₄₅Fe₄₅Zr₁₀)_X(Al₂O₃)_100-X]/[(Co₄₅Fe₄₅Zr₁₀)_X(Al₂O₃)_100-X+O₂]}₃₀₀ multilayer heterogeneous structure has been obtained by ion-beam sputtering method. Magnetostatic and magnetodynamic properties and the structure of the nanocomposites have been investigated. It was shown that, the oxidized interlayer composite adding lead to suppression of perpendicular magnetic anisotropy component, and a change in the magnetic structure of the composites, which determines the change in the frequency dependence of the real (μ^/) and imaginary (μ^//) parts of the complex permeability.