Dependence of magnetization processes on vortex helicities in permalloy nanorings

Two different magnetization reversal processes, which are caused by the helicities of the two small vortex domain walls in the two sides of the onion state, are found numerically to exist in thin film rings. When the two vortex domain walls are in the same helicity, the onion state will transform to flux closure state (vortex state) with increasing of the field, and then transform from the flux closure state (vortex state) to the reverse onion state with further increasing of the field. When the two vortex domain walls are in opposite helicities, however, with increasing of the field, the onion state will transform directly to the reverse onion state skipping the flux closure state (vortex state). (c) 2008 American Institute of Physics.