K. A. Zvezdin

Nonuniformity of a planar polarizer for spin-transfer-induced vortex oscillations at zero field

We discuss a possible mechanism of the spin-transfer-induced oscillations of a vortex in the free layer of spin-valve nanostructures, in which the polarizer layer has a planar magnetization. We demonstrate that if such planar polarizer is essentially nonuniform, steady gyrotropic vortex motion with large amplitude can be excited. The best excitation efficiency is obtained for a circular magnetization distribution in the polarizer. In this configuration, the conditions for the onset of the oscillations depend on the vortex chirality but not on the direction of its core.

Phase transformations of the magnetic structure in film nanobridges

The magnetic structure of a plane nanobridge consisting of two ferromagnetic film electrodes connected by a nanosized crossbar of the same material is studied. Due to their magnetoresistive properties, such bridges are of considerable interest for microelectronics. Using a numerical micromagnetics method, it is shown that a domain wall is displaced from the center of the bridge crossbar as the anisotropy constant of the system decreases and reaches a critical value. A phase diagram is constructed, which makes it possible to determine the possible magnetic states of real nanobridges. The mechanism of the phase transformation is described in terms of an analytical model. This model explains the shape of the phase diagram of the nanobridge. Formally, the transformations of the magnetic structure of the nanocontact can be described in terms of the Landau theory of phase transitions in a certain range of parameters of the system.

Dynamics of Coupled Magnetic Vortices in Trilayer Conducting Nanocylinder

Solving numerically the generalized Landau–Lifshitz equation, we have carried out the micromagnetic investigation of the dynamics of two dipole-coupled magnetic vortices in a trilayer nanocolumn under the action of the external magnetic field directed perpendicular to the sample plane and spin-polarized electric field. The possible existence of different regimes of vortex motion, depending on the polarized current, is demonstrated. The current dependence of the oscillation frequency for the case of stationary dynamics of coupled vortices with the same frequency has been established. The possibility of controlling the frequency of the stationary vortex motion and tuning the control current amplitude by the external magnetic field is shown. Using the analytical method for simplified description of the dynamics of coupled vortices, the current and magnetic-field dependences of the frequency have been obtained, which are qualitatively consistent with the numerical data.

Magnetic-field induced phase transitions in intermetallic rare-earth ferrimagnets with a compensation point

The behavior of highly anisotropic f-d ferrimagnets in strong magnetic fields is studied. HoFexAl12-x (x = 5,6) compounds, which have compensation temperatures Tcomp > 0 for x = 5 and Tcomp ≈ 0 K for x = 6, are used as examples. Magnetic phase diagrams for these substances in a two-sublattice (f-d) ferrimagnet with a compensation point are constructed and analyzed with exchange interactions and anisotropy taken into account. Special attention is devoted to the influence of the rare-earth anisotropy on the form and properties of the phase diagram.

Ferroelectrics of homogeneously deformed rare-earth garnet crystals, excited by elastic wave propagation

The effect of deformation on the electric properties in rare-earth garnet compounds is elucidated. It is shown that inhomogeneous deformation causes the emergence of electric polarization in garnet crystals on account of nonequivalent low-symmetry sites of rare-earth ions in the cubic structure of these crystals, whose symmetry of the environment has no inversion center. The polarization of a rare-earth ion subsystem in garnet crystals is studied upon the elastic wave propagation therein.

Current-induced motion of a domain wall in a multilayer structure: Pressure vs torque

The problem of current-induced motion of a solitary domain wall in a free layer of the spin-valve structure is considered; the current flows perpendicularly to the structure layers. The action of the longitudinal and transverse components of the nonequilibrium polarization of the carriers injected into the free layer on the magnetization is analyzed.