Vol 87, No 4 (2023)

Using the matrix method for solving the linearized Usadel equations, the critical temperature and the distribution of singlet pairing components of the superconductor/ferromagnet/superconductor/ferromagnet structure with nonideal boundaries are obtained. A transition from the π- to the 0-phase state between layers of superconductors was obtained with a change in the angle between the magnetizations of ferromagnetic layers in such a structure.

The structural and electronic properties of Mn₃Z alloys (Z = Ga, Ge) are studied ab initio. It is shown that in the cubic and tetragonal phases, the configuration with antiparallel orientation of magnetic moments of Mn atoms on different sublattices is energetically favorable. Calculations of the electronic densities of states show that the spin polarization of the tetragonal phase is about 60%. The results obtained are in good agreement with the experimental data.

Within the framework of the spin density functional theory, the energy and magnetic properties of Fe/Cr/Fe, Fe/Pt/Fe systems were studied using the VASP software package. Calculations of the dependence of the total energy on the angle of direction of the magnetic moment of atoms showed the advantage of perpendicular anisotropy for Fe/Cr/Fe for all considered Fe film thicknesses and surface orientations. For Fe/Pt/Fe, a more complex dependence is observed, but with an increase in the iron film thickness, easy-plane anisotropy prevails.

Magnetization reversal diagrams are constructed for a longitudinally magnetized film with the parameters of yttrium iron garnet doped with cobalt. The film is excited by nanosecond magnetic field pulses with an amplitude of up to 1000 Oe. It is shown that at a magnetizing field smaller than the anisotropy field, under the action of the pulse field, transitions between stable states, characterized by energy minima, occur.

We studied new structures of superconducting spin valves of Fe2/Nb/Fe1/CoO_x and Fe2/Al₂O₃/Nb/Al₂O₃/Fe1/CoO_x designs. The operation of these structures is built beyond the classical superconductor/ferromagnet proximity effect. The superconductor/ferromagnet interface in these structures is separated by an additional insulating layer. According to the results of our studies, the Fe2/Al₂O₃/Nb/Al₂O₃/Fe1/CoO_x structures are the most promising structures for further research.

We studied two-layer ferromagnet/ferroelectric heterostructures, where iron, cobalt, and nickel were used as ferromagnetic layers, and lithium niobate was used as a ferroelectric substrate. According to our studies, applying an electric field from 10 to 50 V to a ferroelectric lithium niobate substrate is sufficient to register a change in the direction of the magnetization vector of the ferromagnetic layer.

The electrical resistance of Ba_0.8Sr_0.2TiO₃/LaMnO₃/Ba_0.8Sr_0.2TiO₃ film heterostructures has been studied. It is shown that the resistance decreases significantly with a temperature below the maximum temperature of about 170 K. Thus, for such heterostructures, the effect of quasi-two-dimensional conductivity was discovered, but only at certain layer thicknesses.

We investigated the temperature dependence of the permittivity and electrical conductivity of sodium niobate ceramics doped with iron or bismuth in a wide frequency range of the external field. The phase transitions and their characteristics in these solid solutions, as well as the mechanisms of conduction, are determined.

A model of non-stationary charge carrier transport in M/PZT/M ferroelectric structures has been developed. It is assumed that, at room temperature, electrons generated by oxygen vacancies are captured by Ti⁺³ levels and move between them under the action of electric fields caused by the external bias and polarization. The polarization distribution in a PZT film is described with varying degrees of complexity, from a constant value outside the defect layers to one determined by the equation following from the Landau–Ginzburg theory. The numerical simulation performed made it possible to explain the reasons and conditions for the appearance of current–voltage characteristics with unusual current peaks, to show the existence of several solutions in the Landau–Ginzburg model for a film with Schottky barriers, and to reveal the response of charged domain walls to an applied voltage.

Crystal and magnetic structures of Dy_{1 – x}Ho_xMnO₃ multiferroic single crystals (x = 0, 0.2) were investigated by the neutron diffraction methods. It is shown that the substitution of Dy by Ho at the level of 20% does not change the crystal symmetry of the compound. Description was made using the Pbnm group down to very low temperatures for both compounds. Within accuracy of the measurements, magnetic ordering does not change the crystal structure. Substitution of Dy by Ho suppresses spontaneous ordering of a rare-earth subsystem with a propagation vector (0 0.5 0). This leads to a situation when two magnetic subsystems, manganese and rare-earth ones, have a coherent incommensurate space propagation.

We presented ab initio calculations of bulk structures and thin films of hafnium oxide, and heterostructures based on hafnium oxide in the tetragonal phase and silicon, structural and electronic properties are investigated. The density of states spectra is considered, the results obtained are analyzed, and some of them are compared with previously obtained data (for the studied systems).

The effect of variation the length of drift tube of two-section structure of axisymmetric relativistic diffraction generator on its output power operation and sustainability of generation is considered. A comparison is made of the electromagnetic field strength distribution for structures with two types of discontinuity: sinusoidal corrugation and half-torus on pedestal.

A model of modular nonlinearity has been developed for calculating the field of high-intensity bounded acoustic beams. The exact solution of this problem is obtained. The influence of diffraction and nonlinear effects on the time profile is demonstrated. It is shown that as the aperture decreases, a sequence of short positive high-amplitude pulses is formed, which was observed experimentally.