Observation of a non-trivial in-plane field-like torque due to out-of-plane spin polarization in Al/Ni80Fe20/AlOx heterostructures

Abstract

We performed spin-torque ferromagnetic resonance studies on the Al/NiFe/AlOx heterostructure. We observed a large non-trivial field-like torque, τFLz, due to the out-of-plane spin polarization, despite the lack of heavy metal in our multilayer. The torque conductivity is found to be significant with a value equal to σFLz=(21±2)ℏ2e×103 Ω−1m−1. From a detailed Al thickness dependence, we show that τFLz arises from the interface between Al and NiFe. We demonstrate that the observed τFLz arises from the spin-swapping mechanism at the Al/NiFe interface rather than the orbital Hall effect of Al. This observation of a non-trivial spin–orbit torque in the low-cost light element, Al, is highly significant for the energy-efficient control of spintronic devices.