Nonlinear Nonstationary Dynamics of Neel Domain Walls in Ultrathin Films with an In-Plane Anisotropy

Nonlinear dynamic behavior of domain walls in ultrathin films (of thickness b < b(t), where b(t) is a critical thickness below which only one-dimensional Neel 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 b(t) the nonlinear dynamic transformation of the Neel-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.