Stochastic domain-wall depinning under current in FePt spin valves and single layers

In this paper, we report on the current-induced depinning of domain walls from structural defects in nanowires tailored in both FePt//MgO and FePt/Pt/FePt//MgO epilayers with high perpendicular magnetic anisotropy. In these systems, we show that the nature of domain wall depinning is stochastic. Our results indicate that there are two source of stochasticity: thermal activation and domain wall configuration degeneracy. We show that the depinning rate can be influenced with a strong efficiency by an applied dc current, whose effect on both thermal and configurational stochasticity is exactly similar to that of an additional magnetic field. Interestingly, Joule heating is found to cancel the bipolar effect of the current for quite low current densities. Contrarily to what was expected, the spin-transfer efficiency measured in single layers and spin valves are found to be similar. Results from micromagnetic simulations are shown to reproduce the observed statistical trends.