Asymmetry Induced Inhomogeneous Magnetization Reversal in Hemispherical Shells

Abstract

Inhomogeneous magnetic phases like magnetic vortex are expected to open up a wide range of opportunities both from a fundamental and technological perspective. Asymmetric nanostructures offer alternative data storage possibilities by suggesting a control over the vortex formation and thereby chirality [1-3]. Asymmetry introduced in the geometry also has a strong impact on magnetization reversal. Increased coercivity, remanence, and switching field distribution with the degree of asymmetry establishes the existence of an induced anisotropy, which in turn could even destabilize the magnetic vortex depending on the degree of asymmetry in a particular geometry [4]. Following these ideas, in this work, we investigate how the asymmetry modifies the magnetization reversal in hemispherical shells. We address this issue by breaking the symmetry of non-interacting hemispherical cap structures through a thickness modulation inclined at an angle with the symmetry plane and by analyzing the magnetization reversal mechanism for varying thicknesses. Micromagnetic simulations indicate that the asymmetric nanocaps reverse through the propagation of a curling state, while in the symmetric caps, magnetization reversal happens via coherent rotation. With an increase in thickness, the field at which curling state nucleates, shifts towards a higher applied field. The non-uniform magnetization reversal is apparently due to the altered energy contributions resulting from the asymmetry introduced in the nanocaps.