Influence of the asymmetry on reversal process and vortex motion in egg-shaped permalloy plates

Abstract

The reversal processes and vortex motion in asymmetric submicrometer egg-shaped permalloy plates with various aspect ratios are investigated by micromagnetic simulations. The reversal of the magnetization in the egg-shaped plate takes place via nucleation and annihilation of the vortex state. The annihilation of the vortex for larger aspect ratios shows distinct behaviors compared with smaller aspect ratios. The asymmetry of the plate suppresses the reversal via double vortex and coherent rotation for the fields applied along the major axis. An evident change of switching mode is observed at a particular applied field angle. The asymmetric plate achieves control over the rotation sense of the vortex state, and it is dependent on the asymmetry of the plate and the orientation of the external field. The rotation sense of the vortex is clockwise for 0 < θ ≤ 70°, and counterclockwise for θ > 80° as ε = 2 in the sweep-down process. The vortex nucleation and annihilation fields show a strong dependence and different sensitivity on the asymmetry of the plate and field angle.