Enhancement of interfacial spin transparency in Py/NiO/Pt heterostructure

Abstract

This work reports the enhancement of damping-like and field-like spin–orbit torque (SOT) efficiencies and interfacial spin transparency (Tin) in the Py/NiO/Pt heterostructure. The SOT efficiencies and Tin are characterized by combining the spin–torque ferromagnetic resonance (ST-FMR) and the spin-pumping (SP) techniques. The inevitable inverse spin Hall voltage contamination induced by SP in the ST-FMR spectrum is extracted and subtracted by combining additional SP measurements, which allows obtaining accurate SOT efficiencies and Tin. The damping-like and field-like SOT efficiencies vary with the NiO insertion layer thickness, which is a result of the change of Tin. The maximum Tin reaches ∼0.82 for a 0.6 nm-thick NiO layer. This work shows that NiO insertion is an effective method for enhancing Tin and, hence, the SOT efficiency.