Spin torque study of the spin Hall conductivity and spin diffusion length in platinum thin films with varying resistivity

TL;DR

This study investigates how the spin Hall conductivity and spin diffusion length in platinum thin films depend on resistivity, revealing an intrinsic spin Hall effect mechanism and estimating the spin diffusion length based on resistivity data.

Contribution

It provides new experimental insights into the relationship between resistivity, spin Hall efficiency, and spin diffusion length in platinum thin films.

Findings

Peak spin Hall torque efficiency at specific thickness

Monotonic increase of efficiency/resistivity ratio with thickness

Estimated spin diffusion length based on resistivity and scattering mechanism

Abstract

We report measurements of the spin torque efficiencies in perpendicularly-magnetized Pt/Co bilayers where the Pt resistivity $\rho_{Pt}$ is strongly dependent on thickness $t_{Pt}$ . The damping-like spin Hall torque efficiency per unit current density, $\xi^j_{DL}$ , varies significantly with $t_{Pt}$, exhibiting a peak value $\xi^j_{DL}=0.12$ at $t_{Pt} = 2.8 - 3.9$ nm. In contrast, $\xi^j_{DL}/\rho_{Pt}$ increases monotonically with $t_{Pt}$ and saturates for $t_{Pt} > 5$ nm, consistent with an intrinsic spin Hall effect mechanism, in which $\xi^j_{DL}$ is enhanced by an increase in $\rho_{Pt}$ . Assuming the Elliott-Yafet spin scattering mechanism dominates we estimate that the spin diffusion length $\lambda_s = (0.77 \pm 0.08) \times 10^{-15} \Omega m^2 /\rho_{Pt}$.