Tuning Spin-Orbit Torque Generation Via Seed/Heavy Metal Interface Modification

Investigations of spin generation and accumulation at the seed layer/heavy metal interface have remained elusive. In this study, we systematically investigate spin-orbit torque (SOT) switching efficiency with different seed layers X={dielectric MgO, metal Ti} beneath the heavy metal Pt, in the substrate/X/Pt/Co perpendicularly magnetized heterostructures. An enhancement of SOT efficiency has been observed in the heterostructure with Ti seed layer, compared to that of inserting MgO. This is attributed to the high spin absorption in Ti seed layer, less spin reflection from Ti/Pt interface, resulting in more net spin accumulation on Pt/Co interface. Moreover, the SOT-induced Co magnetization switching at zero external magnetic field has been observed in the heterostructure with MgO seed layer, due to the strong spin reflection from the insulating MgO layer. This work provides an in-depth understanding of the impacts of the spin reflection from the X/Pt interface and spin transport with different seed layers, which paves an additional way to tune the spin generation in terms of both magnitude and orientation for pursuing high-performance SOT devices.