Spin Hall torque magnetometry of Dzyaloshinskii domain walls

Spin-orbit coupling at a heavy-metal/ferromagnet interface can generate current-induced torques of several possible symmetries while simultaneously affecting the internal structure of domain walls driven by these torques. Disentangling these effects quantitatively is challenging but essential in order to understand the underlying physics of domain wall dynamics in ultrathin ferromagnets. By using in-plane magnetic fields one can isolate these effects based on symmetry. The authors show that in-plane fields, as well as current-induced torques, cause domain walls to rotate in the plane by up to 90 degrees. This new behavior also presents an important technological paradox: strong DMI is essential to achieve fast current-driven domain wall motion, but it simultaneously distorts domain walls dramatically, limiting their utility in applications. The authors propose a solution to this problem based on tuning spin Hall and Rashba torques at interfaces, whose feasibility is justified by recent measurements of these torques. They also show that in Pt/CoFe/MgO the DMI is surprisingly strong, close to the critical strength required for spontaneous skyrmion formation.