A. N. Kalinkin

Skyrmion lattices in the BiFeO3 multiferroic

This work examines conditions for skyrmion lattice stability in BiFeO3 multiferroic films possessing record high ferroelectric and antiferromagnetic transition temperatures, giant polarization, and a giant magnetoelectric effect. Using analytical and numerical calculations, we demonstrate stability of solitary spin vortices (skyrmions) and skyrmion lattices in BiFeO3 films owing to the Dzyaloshinskii-Moriya interaction. Our results confirm that BiFeO3 can be used as a matrix for chips with ultrahigh data density, up to 10 Tb/cm2.

Application of BiFeO3 and Bi4Ti3O12 in ferroelectric memory, phase shifters of a phased array, and microwave HEMTs

This paper examines the main applications of bismuth ferrite and bismuth titanate and demonstrates their potential applications in spintronics and radioelectronics.

Magnetic and electrical properties of multiferroic BiFeO3, its synthesis and applications

Major ways to improve the magnetic and electrical properties of promising multiferroic BiFeO3 and optimize its synthesis have been studied, and its applications in spintronics, photonics, and magnonics have been discussed.

Toroidal spin ordering in BiFeO3, GaFeO3, and Cr2O3 in the Faddeev model with a magnetic field

The Fadeev model is used for describing the recently discovered toroidal spin ordering in piezoelectric and ferrimagnetic GaFeO3 and piezo- and magnetoelectric Cr2O3 and BiFeO3. A stable toroidal solution of the Faddeev model with the topological charge Q= 1 in an external homogeneous magnetic field was obtained using the trial function method. The energy of a toroid as a function of its radius (R) was determined at various values of the external magnetic field (H). It was shown that the energy minimum is shifted toward smaller R’s with an increase in H. At a critical field value, the torus collapses so that the local spin structure disappears. It is suggested to use magnetic field for controlling the torus size in multiferroics, promising materials of spintronics.

Dipole skyrmion vortices in multiferroic BiFeO3

This paper presents finite difference calculations of a dipole skyrmion vortex in multiferroic BiFeO3 and demonstrates a stabilizing role of electrostatic dipole-dipole interaction. We consider the main approaches to producing vortex lattices in BiFeO3 and their potential applications in spintronics and diptronics.

Advanced Inorganic Materials for Hard Magnetic Media

A review of magnetic materials used in modern hard magnetic media is presented. Advanced materials and technologies, along with conventional ones, are described. The capabilities and prospects of further development of data recording and storage systems are discussed.

Toroidal solitons in magnetic oxides, Bose-Einstein condensates, and other media

We consider toroidal soliton solutions in a number of nonlinear models of field theory (Skyrme, Faddeev, and Higgs models). Such models are used in various areas of solid-state chemistry and physics, chemical physics, astrophysics, and plasma chemistry and physics. The stability of toroidal solitons is shown to have a topological nature. We examine different methods of generating a nonlinear contribution to the Lagrangian in order to insure stability of the torus to collapse. Using the Faddeev and Skyrme models, we analyze the toroidal ordering in Bose-Einstein condensates of 23Na, 39K, and 87Rb alkali-metal atoms, the toroidal structures recently found in the magnetic oxides BiFeO3 and GaFeO3, and potential applications of such structures in spintronics. In addition, we address several critical issues in the chemistry and physics of solitons with high topological charges.

Skyrmion mechanism of hole pairing in the high-Tc cuprates

A topological mechanism of hole localization as two skyrmions in the CuO2 layers of high-Tc superconductors is suggested on the basis of a nonlinear σ model.

Toroidal solitons in magnetic oxides : Faddeev model

Toroidal solutions to the Faddeev model are considered for a topological charge Q = 1 using the method of trial functions. The energy E of a torus is evaluated as a function of its radius R. The energy is shown to pass through a minimum at R = 3.5, which ensures stability of the torus to collapse. The energy of toroidal solitons, E = 42.25, agrees with earlier results and takes into account the curvature energy. The Faddeev model appears to be useful in analyzing the toroidal ordering found recently in GaFeO3-type magnetic oxides.

Phase Transitions in Four-Fermion Models

The most important advances in the physics of four-fermion theories are illustrated using the Nambu–Jona-Lasinio and Gross–Neveu models. Magnetic-field-catalyzed dynamical chiral symmetry breaking is considered, and the magnetic-field effect on the effective fermion mass is assessed. The models in question are used to interpret the recently discoveredPparity breaking in high-Tc superconductors. High-Tc materials are considered in which the superconducting transition can be interpreted within the Gross-Neveu model as due to the formation of Berezinskii–Kosterlitz–Thouless vortex–antivortex pairs. The generalized Gross–Neveu model with superconducting states is described. Examples are presented of nonperturbative kink–antikink solutions in the Gross–Neveu model, and their role in the restoration of spontaneously broken symmetry is discussed. A number of Gross–Neveu models on a sphere are considered with application to C60 fullerenes and related matrices with Tc = 117 K. It is shown that the curvature effect restores chiral symmetry according to the critical phase dependence rc(Tc).