Tailoring The Current-Driven Domain Wall Motion By Varying The Relative Thickness Of Two Heavy Metal Underlayers

Current-driven domain wall motion (DWM) in heavy metal (HM)/ferromagnet (FM)/oxide heterogeneous structures has attracted strong research interests due to its potential applications in novel magnetic memory and logic devices. It has been reported that current-driven DWM can be either along or against the current direction depending on the selection of HM and/or FM materials. Here, we study the current-driven DWM in a perpendicularly magnetized system with two HM underlayers (Pt and W) that are of opposite spin Hall angles. Instead of changing the material, it is observed that domain walls can move along opposite directions by varying the relative thickness of the two underlayers. We attribute such phenomenon to the competition of two spin currents with opposite signs of spin polarization injected into the ferromagnetic layer. More evidence is shown by the spin Hall effect-induced switching under a fixed in-plane field, where opposite switching behaviors are observed for devices with different relative thicknesses of the underlayers.