COMPUTER SIMULATIONS OF MAGNETIZATION REVERSAL DYNAMICS

Abstract

Computer simulations of a two-dimensional lattice of magnetic dipoles are performed on the massively parallel Connection Machine Supercomputer. These lattices constitute a discrete model for thin films of amorphous rare earth-transition metal (RE-TM) alloys, used in erasable optical data storage systems. The simulated dipoles follow the dynamic equation of Landau-Lifshitz-Gilbert. Using mean-field theory, we have calculated the temperature dependence of the subnetwork magnetizations, the effective fields, the gyromagnetic coefficient, and the Gilbert damping parameter. These results are then used in the simulation of the thermomagnetic recording process, where a focused laser beam creates a hot spot and allows an external magnetic field to reverse the direction of local magnetization. Reversed domains are seen to nucleate during cooling of a heated spot with Gaussian spatial profile. In the absence of defects of the size of a domain wall, these nuclei are seen to collapse in low external fields. In contrast, samples with patches of uniform anisotropy and weakened inter-patch exchange form stable reversed domains. Color visualizations of the magnetization distribution show local pinning of the cooling reverse domain on patch boundaries.