Interfacial and bulk spin Hall contributions to field-like spin-orbit torque generated by Iridium

TL;DR

This study measures spin orbit torques in Ir/CoFeB and Ir/Co films, revealing significant interface and bulk contributions to field-like torque, with implications for magnetic switching applications.

Contribution

It quantifies the interface and bulk contributions to spin orbit torque in Ir-based heterostructures, highlighting the role of film thickness and spin diffusion length.

Findings

Ir provides a damping-like spin torque with high efficiency.

Large field-like spin orbit torque observed, mainly from interface effects.

Bulk contribution to field-like torque becomes significant when Ir thickness exceeds 1.6 nm.

Abstract

We present measurements of spin orbit torques generated by Ir as a function of film thickness in sputtered Ir/CoFeB and Ir/Co samples. We find that Ir provides a damping-like component of spin orbit torque with a maximum spin torque conductivity 1.4e5 in SI unit and a maximum spin-torque efficiency of 0.04, which is sufficient to drive switching in an 0.8 nm film of CoFeB with perpendicular magnetic anisotropy. We also observe a surprisingly large field like spin orbit torque. Measurements as a function of Ir thickness indicate a substantial contribution to the FLT from an interface mechanism so that in the ultrathin limit there is a non-zero FLT with a maximum torque conductivity -5.0E4 in the SI unit. When the Ir film thickness becomes comparable to or greater than its spin diffusion length, 1.6 nm, there is also a smaller bulk contribution to the fieldlike torque.