Universal absence of Walker breakdown and linear current-velocity relation via spin-orbit torques in coupled and single domain wall motion

摘要

We consider theoretically domain wall motion driven by spin-orbit and spin Hall torques. We find that itis possible to achieve universal absence of Walker breakdown for all spin-orbit torques using experimentallyrelevant spin-orbit coupling strengths. For spin-orbit torques other than the pure Rashba spin-orbit torque, thisgives a linear current-velocity relation instead of a saturation of the velocity at high current densities. Theeffect is very robust and is found in both soft and hard magnetic materials, as well as in the presence of theDzyaloshinskii-Moriya interaction and in coupled domain walls in synthetic antiferromagnets, where it leadsto very high domain wall velocities. Moreover, recent experiments have demonstrated that the switching of asynthetic antiferromagnet does not obey the usual spin Hall angle dependence, but that domain expansion andcontraction can be selectively controlled toggling only the applied in-plane magnetic field magnitude and not itssign.We show that the combination of spin Hall torques and interlayer exchange coupling produces the necessaryrelative velocities for this switching to occur.