B. N. Filippov

Mobility of domain walls with a two-dimensional distribution of magnetization in magnetic films with in-plane anisotropy

The mobility of asymmetric vortex-like domain walls in magnetically uniaxial films with in-plane anisotropy has been determined as a function of the material parameters and film thickness by numerically solving the Landau-Lifshitz equation with the exact inclusion of the main interactions, in particuar, the dipole-dipole interactions. The data obtained have been compared with those available for one-dimensional models of domain walls, and it has been established that they substantially differ both qualitatively and quantitatively. It has been demonstrated that the two-dimensional models lead to a considerably better description of the experimental data on the domain-wall mobility.

Structure and dynamic properties of asymmetric vortexlike domain walls in inhomogeneous magnetic films with an in-plane anisotropy: I. Equilibrium structures. Nonlinear dynamics in two-layered films

Within the framework of a two-dimensional distribution of magnetization and exact allowance for the basic interactions, including dipole-dipole one, the static properties and nonlinear dynamic behavior of vortexlike domain walls in multilayer magnetically uniaxial films with an in-plane anisotropy have been studied. It has been shown that in such films, just as in single-layer ones, there exist asymmetric vortexlike walls; however, in this case the wall vortices prove to be moved toward the layers with a higher magnetization or toward the layers with a lower anisotropy. At some thicknesses of the layers and magnetization differences in them, the asymmetric Néel walls prove to be unstable. New scenarios of the dynamic transformation of the structure of the walls in multilayer films have been established, which in some cases differ significantly from the appropriate scenarios in the single-layer films.

Nonlinear nonstationary dynamics of Néel domain walls in ultrathin films with an in-plane anisotropy

Nonlinear dynamic behavior of domain walls in ultrathin films (of thickness b < bt, where bt is a critical thickness below which only one-dimensional Néel walls exist in the stable state) has been investigated based on the numerical solution of the Landau-Lifshitz equation with an exact (modelless) allowance for all principal interactions, including dipole-dipole one (in the continuum approximation), in terms of a two-dimensional distribution of magnetization. It is shown that at film thicknesses close to bt the nonlinear dynamic transformation of the Néel-wall structure occurs through the formation of vortex structures. In thinner films, the mechanism of the dynamic rearrangement of the wall proves to be similar to that in unbounded samples. Giant oscillations of the thicknesses of the domain walls in the process of their motion have been revealed. A monotonic decrease in the critical field with increasing b and its nonmonotonic dependence on the saturation induction have been found. The dependences of the period of dynamic transformations of the wall structure on the magnetic parameters and film thickness have been revealed.

Effect of the orientation of the Fe-3% Si crystal surface with respect to crystallographic axes on the dynamic behavior of the domain structure and magnetic losses in rotating magnetic fields

A domain structure and its dynamic transformation in a rotating magnetic field are experimentally studied over a wide induction range (up to 1.7 T) on a single-crystal plate whose surface deviates through angle β from a (110) crystallographic plane. The induction ranges of different dynamic behavior of the domain structure are determined. At an induction below 0.5 T, the magnetization reversal of the plate occurs via a change in the main domain structure. At inductions up to 1.4 T, the main structure undergoes strong dynamic fragmentation. At a higher induction, the magnetization reversal of the sample proceeds via the growth of the closure structure localized at the periphery of the sample in the absence of a magnetic field. The dependences obtained support the early considerations regarding the behavior of magnetic losses.

Magnetic properties and temperature stability of a molybdenum-doped finemet-type alloy

The influence of nanocrystallization conditions on the structure, magnetic properties, and temperature stability of nanocrystalline magnetically soft Fe73.5Cu1Nb1.5Mo1.5Si13.5B9 alloy is studied. It is found that preliminary low-temperature annealing exerts an influence on subsequent nanocrystallization of the alloy. In addition, preannealing followed by nanocrystallization considerably improves the magnetic properties of the alloy. It is shown that the magnetic properties of the material can be controlled by varying the frequency of a magnetic field used for thermal treatment causing nanocrystallization. It is established that the magnetic properties of nanocrystalline Fe73.5Cu1Nb1.5Mo1.5Si13.5B9 alloy offer a high temperature stability.

Structure and dynamic properties of asymmetric vortexlike domain walls in inhomogeneous magnetic films with an in-plane anisotropy: II. Structure rearrangements in three-layer films

On the basis of the numerical solution of the Landau-Lifshitz equations with exact allowance for the fields connected with the exchange, magnetically anisotropic, dipole-dipole, and Zeeman interactions, the nonlinear nonstationary dynamics of vortex-like domain walls in three-layer magnetouniaxial films with an in-plane anisotropy has been studied in some detail. It is shown that the nonlinear dynamic rearrangement of the domain-wall structure occurs with the participation of three- and four-vortex magnetization formations. The origin of various processes has been clarified. As in the case of two-layer films, the appearance of small, in comparison with the period of dynamic transformations of the wall structure, time intervals has been revealed, in which there appear backward motions of the wall. The possibility of the suppression of the nonstationary motion of walls has been established.

Domain structure of a tetragonal antiferromagnet

Abstract A theory of the 90° and 180° domain structure in an easy-plane tetragonal antiferromagnet with nonuniform internal magnetostrictive and mechanical stresses has been developed. The reconstruction of domain structure in an external magnetic field was investigated. Dependencies of critical fields of stability loss of the 90° and 180° domain structures upon a directional external pressure, and magnetostrictive and nonuniform mechanical stresses have been determined. The dependence of the magnetization curve on mechanical stresses has also been determined.

New types of asymmetric domain walls in magnetically triaxial films with a (100) surface

Structure and energy of asymmetric domain walls in magnetically triaxial films with a (100) surface have been studied in a wide range of thicknesses (0.1–2 μm) on the basis of a numerical minimization of the energy functional which exactly takes into account the exchange, magnetically anisotropic, and magnetostatic interactions. It has been established that the structure of asymmetric walls substantially changes with an increase in the film thickness if the anisotropy energy of the film is sufficiently great as, for example, in iron.

Nonlinear Reconfiguration of Vortexlike Domain Walls in Magnetically Uniaxial Films under the Action of an External Field Normal to the Easy Magnetic Axis

The effect of external magnetic field H normal to the anisotropy axis on the energy and configuration of vortexlike asymmetric magnetic walls in a magnetically uniaxial film with an easy magnetic axis parallel to its surface is studied. The investigation is based on minimizing the energy functional of the film with due regard to exchange energy, magnetic anisotropy energy, magnetostatic energy, and Zeeman energy. The range of H below the anisotropy field is found where the asymmetric Néel wall is stable, unlike the case H = 0, when the asymmetric Bloch wall is stable. It is shown that an asymmetric Bloch wall becomes absolutely unstable and reconfigures into an asymmetric Néel wall at some critical values of H = H⊥. The dependences of critical field H⊥ on the film thickness and saturation induction at different values of the anisotropy field are determined: field H⊥ depends on the thickness nonlinearly and on the saturation induction nonmonotonically.

Dynamics of domain walls in magnetically multiaxial films in the thickness range corresponding to the Bloch-Néel transformations of the structure

The numerical minimization of the total energy functional and the solution of the nonlinear Landau-Lifshitz equation have been performed exactly taking into account the fundamental (including dipole-dipole) interactions in terms of the two-dimensional magnetization distribution. The equilibrium structure, energy, mobility, and scenario of the dynamic transformation of the domain walls (in their non- steady-state motion) have been determined as a function of the film thickness b and external magnetic field H for two different ((010) and (110)) orientations of the surfaces of magnetically triaxial films. The range of film thicknesses, including the thickness b = bN, for which the Néel domain walls can be transformed into the Bloch domain walls, has been investigated. The phenomena of anisotropy of the domain-wall energy, the domain-wall mobility, and the period of dynamic transformations of the domain walls have been analyzed as a function of the film thickness b and external magnetic field H. The range of film thicknesses has been determined, in which the non-steady-state motion of the Néel domain walls is accompanied by the creation and annihilation of vortex-like structures despite the one-dimensional character of the magnetization distribution in these walls.