Influence of different onion states on magnetization reversal processes in permalloy rings

Simulation and experiment are performed to investigate the influence of onion states with different-helicity pair vortices on the magnetization reversal process. It is found that for the onion state that has pair vortices with the same helicity, flux-closure state occurs in the reversal process; for the onion state that has pair vortices with opposite helicity, flux-closure state does not occur in the reversal process, and the onion state transforms directly to the reverse onion state. In addition, notches at the same side and diagonal notches with respect to the field direction are designed on the permalloy rings to induce onion states with same-helicity pair vortices and opposite-helicity pair vortices, respectively, for the control of the three-step and two-step magnetization reversal processes.