Large spin current generation by the spin Hall effect in mixed crystalline phase Ta thin films

TL;DR

This study demonstrates that mixed crystalline phase tantalum thin films exhibit a large spin Hall conductivity, which can enhance spin-orbit torque efficiency in heavy-metal/ferromagnetic bilayers, with potential implications for spintronic devices.

Contribution

We report the measurement of high spin Hall conductivity in mixed crystalline phase Ta films, highlighting the role of extrinsic mechanisms and phase control in spin current generation.

Findings

Large spin Hall conductivity of -2439 (ħ/e) Ω^{-1}cm^{-1} in mixed phase Ta.

Strong correlation between crystalline phase, spin mixing conductance, and spin Hall conductivity.

Extrinsic mechanisms dominate spin Hall effect in low-resistivity Ta films.

Abstract

Manipulation of the magnetization in heavy-metal/ferromagnetic bilayers via the spin-orbit torque requires high spin Hall conductivity of the heavy metal. We measure inverse spin Hall voltage using a co-planar wave-guide based broadband ferromagnetic resonance set-up in Py/Ta system with varying crystalline phase of Ta. We demonstrate a strong correlation between the measured spin mixing conductance and spin Hall conductivity with the crystalline phase of Ta thin films. We found a large spin Hall conductivity of $-2439~(\hbar/e)~\Omega^{-1}$cm$^{-1}$ for low-resistivity (68 $\mu\Omega-$cm) Ta film having mixed crystalline phase, which we attribute to an extrinsic mechanism of the spin Hall effect.