Numerical simulations of magnetic materials with MD-GRAPE: Curvature induced anisotropy

Abstract

The time development of an array of magnetic dipoles representing the internal magnetization of a thin film is calculated using a hardware accelerator, MD-GRAPE, for the determination of the magnetic vector potential. The results for single-layer arrays of dipoles are compared with the analogous results obtained from an FFT method and found to be in reasonable agreement. Three-dimensional MD-GRAPE simulations with sinusoidal deformations illustrate the utility of the hardware accelerator in cases that cannot be solved easily with FFT methods. The deformations give the internal field an asymmetry with components parallel to the wave crest, leading to significant changes in the critical external fields required for switching. These changes occur even for small wave amplitudes, comparable to or less than the layer thickness. Layer curvature affects the astroid pattern of critical field strengths by shifting the threshold to lower absolute values of the hard axis field when the curvature is in the easy axis direction, and lower absolute values of the easy axis field when the curvature is in the hard axis direction. This effect of curvature differs from orange peel coupling between two layers because here there is only one layer, and because orange peel coupling shifts the whole astroid pattern as a result of an effective field bias, whereas here the pattern shape is changed without any centroid shift. © 2002 Elsevier Science B.V. All rights reserved.