Field-free spin-orbit torque switching induced by interlayer exchange coupling in Pt/Co/Ru/Ni/Pt multilayer

High-efficient operation of spin-orbit torque (SOT) is central for the exciting field of spin-orbitronics. To realize a deterministic field-free SOT switching, here, we investigate the enhancement mechanism of SOT with the interlayer exchange coupling in a Pt/Co/Ru/Ni/Pt multilayer. We find that the decrease of the domain wall energy in an interlayer exchange coupling system is the pivotal reason for achieving current-induced field-free domain wall switching. Comparing with the direct ferromagnetic couplings, the switching ratio and efficiency present a significant improvement in the interlayer exchange coupling system. Combining micromagnetic simulations and magneto-optical Kerr effect measurements, the domain wall motions are investigated and the switching mechanism is confirmed to be the domain wall depinning regime. Furthermore, the SOT switching direction is proven to be dominated by the field-modulated domain wall motions. This work paves a potential way toward practical spin-orbit torque-based memory, oscillating, and logic devices.