High-throughput techniques for measuring the spin Hall effect

TL;DR

This paper compares high-throughput, lithography-free methods for measuring the spin Hall effect in heavy-metal thin films, demonstrating their effectiveness and consistency with theoretical predictions for rapid material screening.

Contribution

It introduces and evaluates terahertz emission spectroscopy and broadband ferromagnetic resonance as rapid, lithography-free techniques for measuring the spin Hall angle, compared to traditional methods.

Findings

All three techniques produce similar x-dependence of the spin Hall angle.

Quantitative differences are linked to magnetization orientation and interfacial effects.

Results align with first-principles calculations.

Abstract

The spin Hall effect in heavy-metal thin films is routinely employed to convert charge currents into transverse spin currents and can be used to exert torque on adjacent ferromagnets. Conversely, the inverse spin Hall effect is frequently used to detect spin currents by charge currents in spintronic devices up to the terahertz frequency range. Numerous techniques to measure the spin Hall effect or its inverse were introduced, most of which require extensive sample preparation by multi-step lithography. To enable rapid screening of materials in terms of charge-to-spin conversion, suitable high-throughput methods for measuring the spin Hall angle are required. Here, we compare two lithography-free techniques, terahertz emission spectroscopy and broadband ferromagnetic resonance, to standard harmonic Hall measurements and theoretical predictions using the binary-alloy series Au$_x$Pt$_{1-x}$ as benchmark system. Despite being highly complementary, we find that all three techniques yield a spin Hall angle with approximately the same $x$~dependence, which is also consistent with first-principles calculations. Quantitative discrepancies are discussed in terms of magnetization orientation and interfacial spin-memory loss.