Nonlinear dynamics of domain walls with a vortex internal structure in magnetouniaxial films with planar anisotropy

The nonlinear and generally unsteady dynamics of domain walls with a vortex internal structure in a constant magnetic field H is investigated on the basis of the numerical solution of the Landau-Lifshitz equation for a 2D distribution of magnetization M in magnetic films with planar anisotropy taking into account exactly the main interaction, including the dipole-dipole interaction. It is shown that in addition to field H-c (bifurcation field) above which the motion of a wall becomes unsteady and its internal structure experiences global dynamic changes, there exists a field H-0 separating two steady motions of the wall with different structures. The data clarifying the physical origin of the nonlinear dynamic rearrangement of the wall structure are presented. New rearrangement mechanisms associated with the generation and attenuation of vortices as well as their tunneling through the central surface of the wall are established. The existence of subperiod oscillations of the wall velocity in a static field in addition to the oscillations associated with the precession of M around the easy magnetization axis is predicted. The period T of dynamic variations of the wall structure is studied, and an empirical formula is proposed for describing the singular behavior of the T(H) dependence near H = H-c with the critical index depending on the film parameters. The bifurcation process is studied, and a nonlinear dependence of the critical field H-c on the film thickness and the saturation magnetization is established. The possibility of direct experimental investigation of the dynamic rearrangement of the internal structure of the wall is indicated. (C) 2002 MAIK "Nauka / Interperiodica".