Complex THz and DC inverse spin Hall effect in YIG/Cu$_{1-x}$Ir$_{x}$ bilayers across a wide concentration range

TL;DR

This study investigates the inverse spin Hall effect in Cu$_{1-x}$Ir$_{x}$ bilayers across various Ir concentrations, revealing complex behavior and demonstrating ultrafast spin-to-charge conversion capabilities in the terahertz regime.

Contribution

It provides the first comprehensive analysis of the inverse spin Hall effect in Cu$_{1-x}$Ir$_{x}$ over a wide concentration range, highlighting novel non-monotonous behavior and ultrafast spintronic applications.

Findings

Ir concentration dependence shows a minimum and maximum in spin Hall signals.

Both DC and ultrafast stimuli yield consistent results.

Material enables efficient ultrafast spin-to-charge conversion.

Abstract

We measure the inverse spin Hall effect of Cu$_{1-x}$Ir$_{x}$ thin films on yttrium iron garnet over a wide range of Ir concentrations ($0.05 \leqslant x \leqslant 0.7$). Spin currents are triggered through the spin Seebeck effect, either by a DC temperature gradient or by ultrafast optical heating of the metal layer. The spin Hall current is detected by, respectively, electrical contacts or measurement of the emitted THz radiation. With both approaches, we reveal the same Ir concentration dependence that follows a novel complex, non-monotonous behavior as compared to previous studies. For small Ir concentrations a signal minimum is observed, while a pronounced maximum appears near the equiatomic composition. We identify this behavior as originating from the interplay of different spin Hall mechanisms as well as a concentration-dependent variation of the integrated spin current density in Cu$_{1-x}$Ir$_{x}$. The coinciding results obtained for DC and ultrafast stimuli show that the studied material allows for efficient spin-to-charge conversion even on ultrafast timescales, thus enabling a transfer of established spintronic measurement schemes into the terahertz regime.