Determination of the spin Hall angle, spin mixing conductance and spin diffusion length in Ir/CoFeB for spin-orbitronic devices

TL;DR

This study measures key spintronic parameters of Iridium in CoFeB/Ir bilayers, including the spin Hall angle, spin diffusion length, and spin mixing conductance, providing essential data for spin-orbitronic device development.

Contribution

The paper presents the first comprehensive experimental determination of spin Hall angle, spin diffusion length, and spin mixing conductance in Ir/CoFeB bilayers, expanding understanding of Ir's spintronic properties.

Findings

Spin diffusion length in Ir is 1.3 nm at 250 nΩ·m resistivity.

Spin mixing conductance at CoFeB/Ir interface is 30 nm$^{-2}$.

Spin Hall angle of Ir is approximately 2%, similar in sign to Pt.

Abstract

Iridium is a very promising material for spintronic applications due to its interesting magnetic properties such as large RKKY exchange coupling as well as its large spin-orbit coupling value. Ir is for instance used as a spacer layer for perpendicular synthetic antiferromagnetic or ferrimagnet systems. However, only a few studies of the spintronic parameters of this material have been reported. In this paper, we present inverse spin Hall effect - spin pumping ferromagnetic resonance measurements on CoFeB/Ir based bilayers to estimate the values of the effective spin Hall angle, the spin diffusion length within iridium, and the spin mixing conductance in the CoFeB/Ir bilayer. In order to have reliable results, we performed the same experiments on CoFeB/Pt bilayers, which behavior is well known due to numerous reported studies. Our experimental results show that the spin diffusion length within iridium is 1.3 nm for resistivity of 250 n$\Omega$.m, the spin mixing conductance $g_{eff}^{\uparrow \downarrow}$ of the CoFeB/Ir interface is 30 nm$^{-2}$, and the spin Hall angle of iridium has the same sign than the one of platinum and is evaluated at 26% of the one of platinum. The value of the spin Hall angle found is 7.7% for Pt and 2% for Ir. These relevant parameters shall be useful to consider Ir in new concepts and devices combining spin-orbit torque and spin-transfer torque.