Interplay of geometry and magnetic coupling in ferromagnetic nanorings

Abstract

We present a systematic study of angular-dependent magnetization reversal in circular and rounded rectangular Permalloy (Ni₈₁Fe₁₉) nanorings, examining both isolated and strongly interacting arrays using magneto-optical Kerr effect measurements and micromagnetic simulations. Magnetic reversal behavior was analyzed by determining the magnetic fields required for vortex state (VS) nucleation (H_VS1) and vortex state annihilation (H_VS2). For circular rings, increased magnetostatic coupling in more closely spaced nanostructures increased H_VS1 and decreased H_VS2, with the most significant effects observed with applied field aligned with the inter-ring spacing. Rectangular rings exhibit pronounced configurational anisotropy, particularly with field applied near their short axis, where both isolated and coupled arrays display three-step switching behavior and a distinct, angle-dependent enhancement of the VS stable field range. This enhancement spans a broader angular range in coupled arrays and is likely facilitated by the nucleation of vortex core states in areas of high flux curvature and ring width. These findings provide new insights into geometry- and angle-dependent switching in nanorings and highlight their potential in applications such as neuromorphic computing.