Field-free spin-orbit torque switching with enhanced switching ratio in Co/Ni multilayers by laterally broken symmetry induced by He ion bombardment

Abstract Current-induced spin-orbit torque (SOT) provides efficient magnetization control in spintronic devices. However, applications of SOT are limited, as deterministic switching of perpendicular magnetization typically requires an external magnetic field. To overcome this, various approaches have been developed for field-free SOT switching, including lateral symmetry breaking to generate out-of-plane SOT. In this study, we demonstrate field-free perpendicular magnetization switching with a 4-fold enhancement of the switching ratio in [Co/Ni] ferromagnetic multilayers through lateral symmetry modulation of magnetic anisotropy via He ion-irradiation. This approach offers a complementary-metal-oxide-semiconductor integration friendly solution for future SOT-based spintronic devices.