Interfacial spin-orbit torque without bulk spin-orbit coupling

TL;DR

This paper demonstrates that interfacial spin-orbit coupling alone can generate significant spin-orbit torques in metal/insulator interfaces without the need for bulk spin-orbit materials, opening new avenues for spintronic device engineering.

Contribution

It reveals that interfacial Rashba-Eldestein effects can produce spin-orbit torques independently of bulk spin-orbit coupling, and shows how these torques can be tuned via interface engineering.

Findings

Interfacial spin-orbit torque observed in NiFe/Ti/Al₂O₃ structures.

Effective field from interfacial torque exceeds Oersted field.

Insertion of layers modifies the interfacial spin-orbit torque.

Abstract

An electric current in the presence of spin-orbit coupling can generate a spin accumulation that exerts torques on a nearby magnetization. We demonstrate that, even in the absence of materials with strong bulk spin-orbit coupling, a torque can arise solely due to interfacial spin-orbit coupling, namely Rashba-Eldestein effects at metal/insulator interfaces. In magnetically soft NiFe sandwiched between a weak spin-orbit metal (Ti) and insulator (Al$_2$O$_3$), this torque appears as an effective field, which is significantly larger than the Oersted field and sensitive to insertion of an additional layer between NiFe and Al$_2$O$_3$. Our findings point to new routes for tuning spin-orbit torques by engineering interfacial electric dipoles.