Enhancement of the Anti-Damping Spin Torque Efficacy of Platinum by Interface Modification

TL;DR

This paper demonstrates that inserting a thin Hf layer between platinum and a ferromagnetic layer significantly enhances the spin Hall effect's anti-damping torque efficiency by reducing spin pumping without decreasing spin current absorption.

Contribution

It introduces a novel interface modification technique using Hf to boost spin torque efficiency in Pt-based devices, with detailed experimental validation.

Findings

Enhanced spin torque efficiency with Hf insertion.

Suppressed spin pumping at the interface.

No reduction in spin current absorption.

Abstract

We report a strong enhancement of the efficacy of the spin Hall effect (SHE) of Pt for exerting anti-damping spin torque on an adjacent ferromagnetic layer by the insertion of $\approx$ 0.5 nm layer of Hf between a Pt film and a thin, < 2 nm, Fe$_{60}$Co$_{20}$B$_{20}$ ferromagnetic layer. This enhancement is quantified by measurement of the switching current density when the ferromagnetic layer is the free electrode in a magnetic tunnel junction. The results are explained as the suppression of spin pumping through a substantial decrease in the effective spin-mixing conductance of the interface, but without a concomitant reduction of the ferromagnet\' s absorption of the SHE generated spin current.