Magnetization reversal in shape asymmetric permalloy nanocaps

Abstract

Symmetric and asymmetric ferromagnetic permalloy nanocaps of 100 nm diameter are investigated using micromagnetic simulations to study the influence of geometrical asymmetry on the magnetization reversal as a function of thickness. Symmetric nanocaps are featured by having a maximum thickness exactly at the center, whereas, in asymmetric nanocaps, the maximum thickness is at an oblique direction, 20° off to the center of the caps. Magnetization reversal and switching processes in asymmetric nanocaps are found to be strongly dependent on the field direction as well as on the thickness of the nanocaps. In the symmetric nanocaps, magnetization reversal happens via coherent rotation of the magnetic moments. On the other hand, magnetization reversal in asymmetric nanocaps happens via the formation of a non-uniform C-state. An increase in the nucleation field of C-state with the thickness of nanocaps indicates that the stability of the C-state increases with the thickness of the nanocaps. Formation of a C-state due to the shape-induced asymmetry results in distinct M-H loops that depends on the orientation of the nanocaps to the external field direction.