Magnetic state control via field-angle-selective switching in asymmetric rings

Abstract

Ferromagnetic rings have been proposed as an attractive geometry for spintronic storage devices, for instance by storing information in the chirality of the vortex state. Asymmetric rings in particular offer a simple approach to control the vortex-state chirality, and the asymmetry yields additional degrees of freedom for manipulating the states such as by the choice of the field angle with respect to the axes of the system. By using time-resolved scanning electron microscopy with polarization analysis, we directly demonstrate here the influence of the initial magnetization configuration and the field orientation with respect to the ring symmetry axis on the switching mode. The results of experimental imaging are explained by micromagnetic simulations. In particular, for a given field strength we observe switching from the vortex state to the onion state if the symmetry axis of the asymmetric ring is perpendicular to the field orientation. If the symmetry axis deviates slightly from the field orientation, the dynamics change to onion-to-reverse-onion switching with different possible switching pathways. This provides a mechanism for selectively setting different magnetic states by an appropriate choice of the amplitude and orientation of the magnetic field. Furthermore, the angular dependence of the switching is shown to vary with the vortex-state chirality, which could be of use for chirality-dependent logic.