Spin-orbit torque-driven domain wall motion in the absence of Dzyaloshinskii-Moriya interactions

Abstract

The fine structure and dynamics of magnetic domain walls in ultrathin films with perpendicular magnetization, in the presence of a secondary anisotropy, is analysed owing to micromagnetics. Two cases are considered, a cubic anisotropy typical for (111) oriented garnet epitaxial films, and an orthorhombic anisotropy as found in, e.g., Co/W(110) films. The statics is solved first, showing that, in general, domain walls are not of the pure Bloch type. The dynamics under the spin Hall effect induced by a current flowing in an adjacent layer is then monitored. Finite and non-negligible domain wall velocities are predicted in both cases, in the absence of Dzyaloshinskii-Moriya interactions, with distinct behaviours regarding the current density and its orientation with respect to the secondary anisotropy axes. The relevance of these results to recent reports of current-driven domain wall dynamics in insulating ultrathin garnet films, capped with platinum, is discussed.