Size dependence of the spin-orbit torque induced magnetic reversal in W/CoFeB/MgO nanostructures

The spin-orbit torque (SOT) induced magnetic switching in structures such as Hall bars cannot be well explained with the macrospin model. The switching process is affected by the domain wall (DW) dynamics. In previous studies, some observed phenomena, such as intermediate states appearing during the magnetic switching of the Hall bar structure and asymmetric switching currents in two directions, were not well explained. In this letter, by studying the SOT induced magnetic switching in W/CoFeB/MgO nanostructures with different size, these phenomena are demonstrated to be governed by the DW propagations in nanowires and asymmetric DW pinnings at the Hall cross. The size dependence of the switching current is observed and explained with the DW depinning model. These studies provide an approach to detect the properties of the structure, such as the quantification of the spin Hall angle in the heavy metal layer.