Spatially asymmetric switching under spin–orbit torque and Dzyaloshinskii–Moriya interaction

Efficient spin–orbit torque (SOT) switching of perpendicular magnetization is of crucial importance for the magnetic random-access memory. In this work, we study the ultrafast switching of a perpendicular ferrimagnetic alloy by the SOT and an external field (Hx) along the current direction. We find that the magnetization reversal occurs first at the corner of the sample and then propagates to the whole sample through domain-wall motion. We show that, in the absence of field-like SOT, the location of this anti-domain nucleation corner exhibits left-right and top-down asymmetries, as determined by the polarities of current and Hx. By varying the magnitude and sign of field-like SOT, we establish that it significantly affects the switching process but is not necessary for such switching asymmetries. These results are fully explained using a consistent torque analysis framework. Our work improves the understanding of the physics behind SOT switching.