Interfacial spin-orbit torque without bulk spin-orbit coupling

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 (${\mathrm{Al}}_{2}{\mathrm{O}}_{3}$), this torque appears as an effective field, which is significantly larger than the Oersted field and qualitatively modified by inserting an additional layer between NiFe and ${\mathrm{Al}}_{2}{\mathrm{O}}_{3}$. Our findings point to unconventional routes for tuning spin-orbit torques by engineering interfacial electric dipoles.