Blocking and locking during rotational magnetization reversal in ferromagnetic thin films

Abstract

A model describing quasi-static partial rotation and dynamic noncoherent rotation is presented and shown to agree with experiment. It is shown that, with applied field rise times longer than 1 ns, the ripple can be expected to relax in equilibrium with the rotating means magnetization. Magnetostatic stray fields prevent blocking from strongly affecting the rotational process and permit a stable ripple configuration even beyond the critical astroid. At a defined applied field threshold the inhomogeneous portion of the effective field from uniaxial anisotropy and applied field overcomes the stabilizing effects of the magnetostatic stray fields in alternate half-wavelengths of the ripple causing the magnetization there to switch through a large angle. The predicted large angle switching of the magnetization in alternate half wavelengths of the ripple is in good agreement with experimentally observed bands or stripes of reversed and unreversed magnetization both during quasi-static reversals in inverted Permalloy films and during dynamic non-coherent rotation with applied field rise times longer than 1 ns in normal Permalloy films. The model presents a reasonable fit to the field dependence of the angle between the observed stripes and the uniaxial anisotropy axis. Magnitudes of the local anisotropy causing the ripple are obtained from the fit to the data and shown to agree with the values determined by transverse susceptibility measurements.