Nonlinear dynamic structure rearrangement of vortexlike domain walls in magnetic films with in-plane anisotropy

The nonlinear dynamic behavior of vortexlike domain walls in magnetic uniaxial films having an in-plane anisotropy was investigated within a rigorous micromagnetic approach in the framework of a two-dimensional magnetization distribution by numerically solving the Landau–Lifshitz equations (with the Gilbert damping parameter) with allowance for all the main interactions, including the dipole–dipole one. The studies were carried out on magnetic soft films with an anisotropy axis lying in their plane in a dc magnetic field parallel to an easy axis and a pulsed magnetic field normal to it. New possibilities for controlling the nonlinear dynamic rearrangement of the internal structure of domain walls and their velocities in fields both above and below the critical field are established. The wall motion in the field above the critical one is nonstationary.     

Three-dimensional simulation of nonlinear dynamics of domain walls in films with perpendicular anisotropy

A three-dimensional computer simulation of static magnetization configurations and dynamic processes occurring in a domain wall moving in a uniaxial magnetic film with perpendicular anisotropy has been performed based on the numerical solution of Landau–Lifshitz–Gilbert equations. The calculated static states correspond to a domain wall containing Bloch lines with a surface magnetization distribution that depends on the thickness of the film. It has been shown that these structures can be characterized by particular values of the homotopy index. It has been found that the vortex and antivortex structures existing in the bulk of the film form vortex filaments. A method has been proposed for visualization of the joint motion of vortex filaments and Bloch points, which is based on the numerical calculation of the homotopy index and the winding number.     

Spin polarized current controlled dynamics of domain walls in magnetic films with in-plane anisotropy

We study the dynamic properties of asymmetric vortex Bloch walls and classical 1D Néel walls controlled by a spin-polarized current in magnetic films with in-plane anisotropy. It is shown that fairly high velocities of domain walls (up to 100 m/s) can be obtained for the current density in the range j = 10⁶–10⁸ A/cm². The nonlinear dependence of the wall velocity on the film thickness and the linear dependence of the velocity on the current density and inverse damping parameter are found.     

Nonlinear dynamics of vortex-like asymmetric domain walls in magnetic triaxial films

On the basis of numerical solution of the Landau-Lifshitz equation, we investigated the nonlinear dynamic behaviour of 90-degree and 180-degree asymmetric vortex-like domain walls in single-crystal films with cubic symmetry. Films with surfaces of (100) and (110) types are considered. The nonlinear dynamic rearrangement of the internal structure of a wall was investigated. The surface uniaxial magnetic anisotropy is shown to strongly influence the very process of dynamic rearrangement in the internal structure of a wall even up to the complete suppression of the whole process.     

Nonlinear dynamics of domain walls with cross-ties

The dynamic behavior of a domain wall with cross-ties is analyzed on the basis of micromagnetic simulation with exact allowance for all main (exchange, magnetoanisotropic, and magnetostatic) interactions in thin magnetically uniaxial ferromagnetic films with planar anisotropy. It is found that the peculiarities of motion of such domain walls are closely related to the behavior of topological defects in the magnetization distribution (generation, motion, and annihilation of vortex–antivortex pairs on the film surface and Bloch points). We observe three different regimes of motion (stationary, periodic, and turbulent regimes), each of which is realized in a certain range of fields oriented along the easy magnetization axis. It is shown that the experimentally observed dynamic bends of the walls with cross-ties are determined by the type of motion of vortices and antivortices. The velocities of domain walls in different regimes are calculated, and the dynamic configurations of the magnetization and existing dynamic transitions between them are investigated.     

Role of induced anisotropy in the formation of a periodic fine structure of domain walls in films with oblique anisotropy

The influence of induced anisotropy on the formation of a periodic fine structure in domain walls in films with oblique anisotropy with a change in the tilt angle of the easy-magnetization axis at different film thicknesses has been investigated. On the basis of numerical methods, the theoretical results obtained are compared with the experimental data.     

Unidirectional anisotropy of the velocity of domain walls in ferrite-garnet films

A mechanism to explain the gigantic unidirectional anisotropy of the velocity of domain walls, which includes the local rotation of the magnetization in front of a moving domain wall, initiated by radiated spin waves is proposed. Institute of General Physics, Russian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 45–48, September, 1997.     

Transverse and vortex domain wall structure in magnetic nanowires with uniaxial in-plane anisotropy

Micromagnetic and analytical models are used to investigate how in-plane uniaxial anisotropy affects transverse and vortex domain walls in nanowires where shape anisotropy dominates. The effect of the uniaxial anisotropy can be interpreted as a modification of the effective wire dimensions. When the anisotropy axis is aligned with the wire axis (θ(a) = 0), the wall width is narrower than when no anisotropy is present. Conversely, the wall width increases when the anisotropy axis is perpendicular to the wire axis (θ(a) = π/2). The anisotropy also affects the nanowire dimensions at which transverse walls become unstable. This phase boundary shifts to larger widths or thicknesses when θ(a) = 0, but smaller widths or thicknesses when θ(a) = π/2.     

Chaotic dynamics of interacting domain walls in uniaxial ferromagnetic films

The nonlinear dynamics of a periodic system of interacting domain walls in a thin ferromagnetic uniaxial film with transverse anisotropy is examined. The interaction between the domain walls takes place through the magnetostatic demagnifying fields of the domains. The equations of motion derived for such a system of walls are solved numerically by a 4–5th-order Runge-Kutta scheme, while the uniformity of the distributions of the phase trajectory, the form of the Poincaré cross section, and the spectral density of the vibrations serve as indicators of the type of oscillations. All the known types of oscillations are observed in a computer simulation of this nonlinear system: periodic, quasiperiodic, and chaotic. The computational results have a universal character for uniaxial, highly-anisotropic ferromagnetic films having a strip domain structure, since the results can be easily scaled for materials with different magnetic characteristics. Fiz. Tverd. Tela (St. Petersburg) 39, 2036–2039 (November 1997)     

New types of domain walls with vortex-like structure in magnetically multiaxial films

New types of asymmetric vortex-like domain walls have been revealed on the basis of the two-dimensional model of magnetization distribution, by numerical minimization of the total energy functional of a magnetically triaxial (in particular, multilayer) films with (110) surfaces.     

Asymmetry in the dynamics of domain walls in thin exchange-coupled ferromagnetic films

The kinetics of remagnetization after magnetic field switching was studied by the magneto-optic visualization technique in the bilayer hybrid structure composed of exchange-coupled FeNi and FeMn films. It was observed that not only the static but the dynamic characteristics of remagnetization as well depend on the polarity of a field applied along the direction of easy magnetization. The rate of the process was found to be exponentially dependent on the field strength in both directions, but the rate varied by factors of 10 upon inversion of the field. It was shown that this difference is the consequence of variation of both the time of domains nucleation and the velocity of domain walls motion.     

Complex domain structure in a magnetic film with oblique anisotropy

Analytical formulas have been derived to calculate the distortion of the stripe domain structure in a ferromagnetic film under the action of a bubble domain formed in this film. On the basis of the formulas obtained, an experimentally obtained domain configuration has been calculated. The results of the calculation coincide with the observation data within the experimental error.     

Diffraction of light from a stripe domain structure with tilted domain walls

The intensity and polarization parameters of light waves diffracted from a stripe domain structure with tilted domain walls and the magnetic moment in domains oriented parallel to the walls are determined in the approximation of thin layers and linear magnetooptical coupling.     

Experimental investigation of the magnetic structure of domain walls in thin ferromagnetic films

The structure of domain walls in thin magnetic films has been studied by the Lorentz method using electron microscopy. The possible existence of the coinciding and opposite directions of rotation of the magnetization vector in Néel domain walls has been proved experimentally. The domain walls separating 90° domains have been found in single-crystal magnetic films. These walls consist of domains with a considerably smaller area than 90° domains.     

Effect of a pulsed magnetic field on the nonlinear dynamics of vortexlike domain walls in magnetic films

The Landau-Lifshitz equation is numerically solved to study the nonlinear dynamic behavior of domain walls with the 2D vortexlike magnetization distribution in magnetically uniaxial films that have in-plane anisotropy and are exposed to a pulsed magnetic field. It is shown that a pulsed magnetic field H _p may induce transitions between various steady wall motions that differ in magnetization distribution. Solitary rectangular pulses, as well as a regular train of rectangular pulses, may be used to control the period of nonlinear dynamic transformations of the wall internal structure and the related period of variation of the wall velocity.     

Nonlinear waves in a chain of plane-parallel domain walls in ferromagnets

Taking into account the nonlinear interaction between plain domain walls (DWs) in a chain of DWs, one-and two-parameter solitons are obtained. These solitons are solitary shear waves propagating along the DW chain.