Monte Carlo simulation of the effects of the local variation of the coercivity in magneto-optic media

Abstract

Monte Carlo simulations on a two-dimensional lattice of magnetic dipoles have been performed to investigate the effects of local variations of the nucleation and domain-wall coercivity on the magnetic reversal by thermal activation in thin films for magneto-optic storage. The results of the simulations are in good qualitative agreement with experimental observations; the rounding of the hysteresis loops, the inhomogeneous distribution of small regions of unreversed magnetization in the interior of a domain, the directional preference of the domain wall motion resulting in the distortion of the domain shape and the enhancement of the jaggedness of the domain boundary surface. The fractal dimension of the domain wall remains a good figure of merit of the smoothness of the domain boundary. The distribution of coercive fields is correlated to the abruptness of the transition of the wall motion from a thermo-activated to a viscous process, when the external field or coercivity is varied. The model is useful for the characterization of domain growth in rare-earth–transition-metal (RE–TM) and also to some extent in ultrathin and multilayered films.