Magnetization reversal in asymmetric Co rings studied by micromagnetic simulation

Previous simulation reports have shown that the magnetization reversal mechanism in the asymmetric rings with the global vortex state is dominated by domain wall movement. This work investigates the asymmetric Co rings with relatively large sizes and thick arms with simulation. Results show that the magnetization reversal processes are dominated by the formation, movement, and annihilation of localized vortex states. 90 degrees decenter of the inner core is favorable for a stable global vortex state with controllable chirality. Either a larger 90 degrees decenter distance or a thicker thickness brings about a higher stability of global vortex state. However, the global vortex state cannot be obtained at remanence in these rings. In the smaller rings, with the global vortex state obtained at remanence, the stability of global vortex state is enhanced when the inner core size grows larger, and it is due to the reduced possibility of the formation of localized vortex state. (C) 2014 AIP Publishing LLC.