Current-induced domain-wall motion in permalloy semi rings

We have incorporated the model of Zhang and Li [Phys. Rev. Lett. 93 (2004) 127204] for spin-transfer torque into the Landau-Lifshitz-Gilbert equation and have investigated the current-induced magnetization dynamics of permalloy (Ni80Fe20) semi rings. The distribution of the current density within the ring is taken into account. Current-induced eigenmodes with distinct resonance frequencies and higher harmonics are observed as well as a dependence of the resonance frequency on the ring radius. The domain-wall mass determined from the micromagnetic simulation and an analytical model is in agreement with recent experiments. Maximum domain-wall velocities between 30 and 34ms-1 are deduced