Surface Roughness Effects on Magnetization Reversal of Magnetic Ring Elements
The effect of surface roughness on magnetoresistance of permalloy ring structure is investigated. Microstructured permalloy rings with surface roughness varying from 4.2 to 21 nm were fabricated using electron beam lithography and a chemical etching process. It is found experimentally that the first and second nucleation fields decrease obviously with the surface roughness increasing, and the field range for the flux-closure state is not associated with surface roughness. The results indicate that surface roughness in permalloy ring structure is an important factor that influences the magnetic behaviors of the ring. This result can provide important information for future designs of ring-shaped magnetic devices.
Angular arrangements of triangular fins for controlling the magnetization processes in permalloy rings
The influences of triangular fins’ positions on controlling the magnetization processes are investigated. It is observed experimentally that when the included angle between the triangular fins and the field direction is 15° or 30°, the magnetization reversals are repeatable in the sweep-up and sweep-down processes, and the magnetization processes are controllable. In contrast, when the included angle between the triangular fins and the field direction is 45° or 60°, the magnetization reversals are unrepeatable and random in the sweep-up and sweep-down processes. Magnetization reversal can only be controlled when positions of the triangular fins are close to the original nucleation regions of the rings. When triangular fins are away from the original nucleation regions, two kinds of magnetization reversals randomly occur without being controlled by the artificial nucleation sites, and the triangular fins thus lose their control ability.
Vortex circulation control in mesoscopic ring magnets
We present a simple method to control the direction of the circulation of the magnetization in mesoscopic ring magnets, using a uniform magnetic field only. The method is based on the nucleation free switching which occurs when the rings switch from the near-saturated state, referred to as the “onion state,” to the flux-closed vortex state. Two possible onion states, forward or reverse magnetized, are possible for a given direction of the magnetic field. Going from the forward or the backward onion state, both local scanning Kerr microscopy measurements and micromagnetic simulations show that the clockwise or the counterclockwise vortex state, respectively, can be selected due to asymmetric pinning of the two domain walls that are present in the onion state.