Partial Rotation in Permalloy Films

Abstract

Magnetization reversal at an angle to the easy direction has been studied on Permalloy films with different values of coercive force H_c and anisotropy field H_K. The hysteresis properties show that ``inverted'' films (H_c>H_K) do not represent a special case, but that every film exhibits inversion in a certain sector of field direction. In the inversion sector, two critical field values are observed. The corresponding Bitter patterns make it evident that the lower critical field is due to a partial rotation process which is accompanied by a splitting of the film into many fine domains, whilst the higher one is due to wall motion. The observed processes can be understood qualitatively if the dispersion of the local values of the anisotropy field and anisotropy direction, as well as the internal exchange and stray field coupling are taken into account.