Numerical simulation of thermomagnetic writing in RE-TM films

Abstract

In the development of high-performance magneto-optic (MO) media for data storage, it is important to understand the processes by which reversed magnetic domains are formed in thermomagnetic writing. Thin films of amorphous rare earth-transition metal (RE-TM) alloys deposited by sputtering on a nonmagnetic substrate have become a popular choice for an erasable storage medium. We have developed a simplified micromagnetics simulation of the behavior of RE-TM films that produces an equilibrium configuration of film magnetization for a specified thermal profile and applied magnetic field. This Monte Carlo-type model is useful for assessing the size, shape, and stability of written marks in MO recording. In addition, the simulation provides estimates of the minimum field strength required for nucleation and growth of reversed domains, and hence it predicts film coercivity at any temperature. An equilibrium state is determined by magnetic energy minimization. Magnetization dynamics are not incorporated into the model, but instead, a quasi-static approach to equilibrium is simulated. Spatial resolution can be arbitrarily small, and discretization down to about 20 nm can be reasonably accommodated. Readout of written domains has been incorporated as an additional feature of this model.