Spin-transfer-torque-driven domin-wall dynamics in Permalloy nanowires

Pulse-current-driven domain-wall (DW) dynamics in Permalloy nanowires are studied using high-temporal-resolution magneto-optical techniques. The time-resolved measurements reveal prompt displacements proportional to current density above a well-defined threshold and yield values of DW velocity and spin-flip efficiency that are a factor of 10 higher than those determined in prior experiments. A stochastic variation in the wall displacements associated with termination of the current pulse is observed. The experimental results suggest the presence of both adiabatic and nonadiabatic spin-transfer-torque mechanisms, but do not appear to be fully explained by existing theoretical models.