Parametrically forced sine-Gordon equation and domain wall dynamics in ferromagnets

A parametrically forced sine-Gordon equation with a fast periodic mean-zero forcing is considered. It is shown that π kinks represent a class of solitary-wave solutions of the equation. This result is applied to quasi-one-dimensional ferromagnets with an easy-plane anisotropy, in a rapidly oscillating magnetic field. In this case the π-kink solution we have introduced corresponds to the uniform ``true'' domain-wall motion, since the magnetization directions on opposite sides of the wall are antiparallel. In contrast to previous work, no additional anisotropy is required to obtain a true domain wall. Numerical simulations showed good qualitative agreement with the theory.