Observation of Multiple Transitions on Permalloy Ring by Magnetic Force Microscopy

[[abstract]]We present a study of magnetization reversal on microstructured permalloy thin film rings using a magnetic force microscopy in the presence of external magnetic fields up to 540 Oe. Permalloy rings with fixed thickness/outside diameter of 23 nm/5 μm and inside diameter of 2.2 and 2.6μm, respectively, were fabricated by using standard electron beam lithography through a lift-off process. Four transitions during magnetization reversal were observed on the one with 2.2 μm inside diameter, in which the magnetization was evolved from onion to vortex-pair, vortex-pair to vortex, vortex to vortex-core, vortex-core to reverse onion state. The remanent state was flux closure vortex state. A similar magnetization evolution occurred on the one with 2.6 μm inside diameter except that the remanent state was vortex pair. The numerical simulation results using OOMMF showed good agreement with the experimental results. These multiple stable states during the magnetization reversal may provide an excellent opportunity for developing multi-bit storage cells