Terahertz spectroscopy for all-optical spintronic characterization of the spin-Hall-effect metals Pt, W and Cu$_{80}$Ir$_{20}$

TL;DR

This paper introduces a terahertz spectroscopy method to efficiently characterize spin-Hall-effect metals, enabling the extraction of key spintronic parameters and providing insights into interface effects in magnetic heterostructures.

Contribution

The study develops a novel all-optical terahertz spectroscopy technique for measuring spin Hall angle and spin-current relaxation length in metals, validated against literature data.

Findings

Terahertz spectroscopy effectively measures spintronic parameters.

Interface effects on spin-current transmission are minimal.

Good agreement with existing DC measurement data.

Abstract

Identifying materials with an efficient spin-to-charge conversion is crucial for future spintronic applications. The spin Hall effect is a central mechanism as it allows for the interconversion of spin and charge currents. Spintronic material research aims at maximizing its efficiency, quantified by the spin Hall angle $\Theta_{\textrm{SH}}$ and the spin-current relaxation length $\lambda_{\textrm{rel}}$. We develop an all-optical method with large sample throughput that allows us to extract $\Theta_{\textrm{SH}}$ and $\lambda_{\textrm{rel}}$. Employing terahertz spectroscopy, we characterize magnetic metallic heterostructures involving Pt, W and Cu$_{80}$Ir$_{20}$ in terms of their optical and spintronic properties. We furthermore find indications that the interface plays a minor role for the spin-current transmission. Our analytical model is validated by the good agreement with literature DC values. These findings establish terahertz emission spectroscopy as a reliable tool complementing the spintronics workbench.