V. A. Orlov

A comparative analysis of the mechanisms of pinning of a domain wall in a nanowire

A comparative analysis of the influence of random fluctuations of the crystallographic anisotropy and surface roughnesses on the pinning of a domain wall in a nanowire has been performed in the framework of the model of a polycrystalline nanowire. The initial magnetization curve and the coercive force for these mechanisms of pinning have been calculated. A criterion has been formulated according to which surface inhomogeneities of the nanowire play the key role in the process of pinning of a domain wall. The analytical results obtained have been verified using computer simulation.

On the Properties of a Stochastic Magnetic Structure of Low-Dimensional Ultradisperse Ferromagnets

Analysis is given of the effect of the dimensionality of structural inhomogeneities on the properties of the magnetic structure of ultradisperse ferromagnetic materials. The coordinate dependence of the magnetization dispersion of magnets with one-dimensional and two-dimensional inhomogeneities of magnetic anisotropy has been calculated. The linear dimension of a magnetic block for one-and two-dimensional inhomogeneities of the anisotropy field has been estimated. A method for exact calculation of the distribution function of magnetization rotations in the block is suggested.

Properties of effective anisotropy of magnetic blocks in ultradisperse ferromagnets

Parameters of effective anisotropy of ultradisperse ferromagnets have been studied with allowance for the block structure of magnetization. Analytical relationships for the first and second effective anisotropy constants of the blocks have been obtained. An analysis of the influence of various types of inhomogeneities in the local-anisotropy field on the parameters of the block structure and spin-reorientation phase transitions has been performed. The dependences obtained have been tested by computer-aided simulation.

Magnetostatics dualism in a one-dimensional chain of classical magnetic moments

Magnetostatic interaction in polycrystalline nanowires manifests itself in two competing ways, providing the existence of a stable domain structure even in the absence of exchange interaction between crystals. It has been found that not only the domain structure but also the block magnetization structure of the nanowire consisting of exchange-noninteracting crystallites are of magnetostatic nature. The average domain wall width and magnetization correlation length have been calculated analytically and validated by simulation. The feasibility of the “easy axis” and “easy plane” phases of the effective anisotropy for different crystallite shapes has been demonstrated.

Statistics of magnetization jumps in nanowires

The model of a polycrystalline nanowire has been used to theoretically solve the problem of searching for the distribution function of the following characteristics of the magnetization process: the field of the start of a domain wall; and the magnitudes of Barkhausen macro- and microjumps. The results have been tested using computer simulation.

Ground state of the magnetization of nanowires

Analytical and numerical methods have been used to study the ground state of magnetization of a nanowire consisting of ferromagnetic crystallites that are coupled via exchange interactions. The random nature of the field of crystallographic anisotropy has been taken into account. It is shown that the magnetization of a nanowire is divided into weakly interacting regions of magnetization called blocks. Such characteristics, as the average size of a magnetic block, its effective anisotropy constant, and their dependence on the size of crystallites have been calculated analytically and simulated numerically in a two-angle approximation. The coordinate dependences of the magnetization dispersion at the edge and in the bulk of the magnet have been determined. It is shown that the functional dependence of the dispersion on the coordinate changes with moving away from the free edge of the nanowire.

Correlation properties of the stochastic magnetic structure of ultradispersed ferromagnetic materials

The properties of the stochastic magnetic structure of ultradispersed ferromagnetic materials are studied. The correlation coefficients of the magnetization of a magnetic material are calculated for various types of chaos in the anisotropy field. The effects of different types of disorder on the parameters of a stochastic magnetic structure are compared. Numerical simulations by various methods confirm the theoretical results.

On magnetization stability of ferrimagnetic nanocylinder in ferroelectric matrix

The model of a composite material with ferrimagnetic nanocylinders embedded into the dielectric matrix has been considered theoretically. The problem of the influence of mechanical stresses that arise in the composite upon the application of an electric field on the magnetic parameters of the inclusions has been investigated. The conditions under which the spin-reorientation transitions are made possible have been determined.

Formation of a given distribution of anisotropy axes in ferromagnets with regular inhomogeneities

The possibility for forming a given direction distribution of effective anisotropy axes of magnetic blocks is studied in one-dimensional nanogranular structures with alternating directions of local anisotropy axes of crystallites. Analytical expressions are derived for the direction distribution density of effective axes. It is shown that the direction of the anisotropy axes of magnetic blocks is very sensitive to the size of ferromagnetic grains and the degree of misorientation of local axes. Computer simulation is used to verify the derived direction distributions of effective axes of blocks.

On the theory of the thermofluctuation motion of domain walls in nanowires

Using the Arrhenius law, the thermofluctuation motion of a domain wall in a nanowire in the field of energy barriers formed by magnetic nonuniformities is investigated. The expression for the density of the distribution of the activation energy in the case of the domain wall pinning at magnetic nonuniformities has been obtained. The velocity of the thermally activated motion of the domain wall for certain particular cases of the probabilistic distribution of the activation energy has been estimated.