Possible sources of coercivity in thin films of amorphous rare earth-transition metal alloys

Abstract

Computer simulations of a two-dimensional lattice of magnetic dipoles are performed on the Connection Machine. The lattice is a discrete model for thin films of amorphous rare earth-transition metal alloys, which have application as the storage media in erasable optical data storage systems. In these simulations the dipoles follow the dynamic equation of Landau–Lifshitz–Gilbert under the influence of an effective field arising from local anisotropy, near-neighbor exchange, classical dipole–dipole interactions, and an externally applied field. The effect of random axis anisotropy on the coercive field is studied and it is found that the fields required for the nucleation of reverse-magnetized domains are generally higher than those observed in the experiments. Various ‘‘defects’’ are then introduced in the magnetic state of the lattice and the values of coercivity corresponding to different types, sizes, and strengths of these ‘‘defects’’ are computed. It was found, for instance, that voids have insignificant effects on the value of the coercive field, but that reverse-magnetized seeds of nucleation, formed and stabilized in areas with large local anisotropy, can substantially reduce the coercivity.