Micromagnetic predictions of closure domain patterns in magnetic thin films

The magnetic domain structures of permalloy thin films have been calculated using a micromagnetic model. The films are assumed to be very thin (500 Å), so that the magnetization lies in the plane of the film. The model takes a small sample of the film, typically several microns in size, and discretizes it into several thousand elements. The total energy of the system is then minimized to obtain the equilibrium states. A restart procedure is designed to overcome the stiff convergence problem in the calculations for the soft magnetic materials. The closure domain patterns predicted are in agreement with experiments and are shown to have advantages compared with domain-level calculations. Disadvantages are that the computation takes an enormous amount of CPU time owing to the large number of unknowns, and that its application is limited to small samples to avoid having an excessive number of grid points