Asymmetric velocity and tilt angle of domain walls induced by spin-orbit torques

Abstract: We present a micromagnetic study of the current-induced domain wall motion in perpendicularly magnetized Pt/Co/AlOx racetracks. We show that the domain wall velocity depends critically on the tilt angle of the wall relative to the current direction, which is determined by the combined action of the Dzyaloshinskii-Moriya interaction, damping-like, and field-like spin-orbit torques. The asymmetry of the domain wall velocity can be controlled by applying a bias-field perpendicular to the current direction as well as by the current amplitude. As the faster domain walls are expelled rapidly from the racetrack boundaries, we argue that the domain wall velocity and tilt measured experimentally depend on the timescale of the observations. Our findings reconcile the discrepancy between time-resolved and quasi-static domain wall measurements in which domain walls with opposite tilts were observed and are relevant to tune the velocity of domain walls in racetrack structures.