Domain-wall dynamic transitions in thin films

Abstract

Two-dimensional domain-wall configurations and dynamics in thin films with the easy axis parallel to the film plane are calculated by using LaBonte-like energy minimization as well as solving the Landau-Lifshitz equation with phenomenological damping. Under a sufficiently small uniform field applied in the easy direction, the effective wall mass and the viscosity coefficient induced from a uniform wall motion are compared with theoretical values. For external fields much greater than the anisotropy field, the wall motion exhibits complex features, including periodic transitions between asymmetric Bloch and Néel wall structures and the emergence of multivortices, depending on the film thickness. The latter serves as a precursor to turbulent wall dynamics at even higher external fields. With a varying external field applied in the hard direction and parallel to the film surface, wall structure changes between asymmetric Bloch- and Néel-type walls are also seen. An irreversible transition is observed which causes a constricted hard-axis hysteresis loop. Dynamically, this hysteretic transition can be associated with wall creep.