Current-induced spin-orbit field in permalloy interfaced with ultrathin Ti and Cu

TL;DR

This study reveals a significant field-like spin-orbit torque in permalloy sandwiched with ultrathin Ti or Cu, likely due to interfacial effects like Rashba-Edelstein, despite weak intrinsic spin-orbit coupling.

Contribution

It demonstrates the emergence of a strong field-like spin-orbit torque in weak spin-orbit materials through interface engineering with ultrathin Ti and Cu layers.

Findings

Spin-orbit field opposes Oersted field in the structures.

Spin-orbit field magnitude is at least three times larger than Oersted field.

No significant damping-like torque observed in the experiments.

Abstract

How spin-orbit torques emerge from materials with weak spin-orbit coupling (e.g., light metals) is an open question in spintronics. Here, we report on a field-like spin-orbit torque (i.e., in-plane spin-orbit field transverse to the current axis) in SiO$_2$-sandwiched permalloy (Py), with the top Py-SiO$_2$ interface incorporating ultrathin Ti or Cu. In both SiO$_2$/Py/Ti/SiO$_2$ and SiO$_2$/Py/Cu/SiO$_2$, this spin-orbit field opposes the classical Oersted field. While the magnitude of the spin-orbit field is at least a factor of 3 greater than the Oersted field, we do not observe evidence for a significant damping-like torque in SiO$_2$/Py/Ti/SiO$_2$ or SiO$_2$/Py/Cu/SiO$_2$. Our findings point to contributions from a Rashba-Edelstein effect or spin-orbit precession at the (Ti, Cu)-inserted interface.