The rate of domain growth in magneto-optic recording media (abstract)

Abstract

The magnetization reversal in magneto-optic media occurs in general by a process of nucleation followed by domain growth. The rate of domain growth is of importance in thermomagnetic recording. Under steady external field conditions, a slow thermoactivated domain growth is observed and the time dependence curves M(t) are often described using a theory by Fatuzzo. The Fatuzzo theory assumes a constant rate of expansion v of cylindrical domains; however, it does not consider the dispersion in the energy barriers or the formation of dendritic domain structures that may arise, for example, from the spatial and temporal variations of the demagnetizing field. Monte Carlo simulations of domain growth were performed using a model that considers distinct intrinsic energy barriers for nucleation and wall motion and incorporates the contribution of the demagnetizing and domain wall energy in the computation of the energy barriers. The rate of domain expansion, v=dRg/dt, where Rg is the radius of gyration, was found to be constant during the initial stage of the growth process but decreases for large Rg as a result of the reduction in demagnetizing strength. Small fluctuations in v are observed arising from the variation of the domain shape during the growth process. The simulations have also shown that the dependence on the applied field is exponential, v=v0 exp(H/Hf), where Hf is the fluctuation field, in good agreement with experiment. The exponential dependence was found to be valid even in the case of dendritic domain growth, suggesting that the Fatuzzo theory may be useful in the description of the growth of domains of irregular shape.