Efficient generation of spin currents by the Orbital Hall effect in pure Cu and Al and their measurement by a Ferris-wheel ferromagnetic resonance technique at the wafer level

TL;DR

This paper introduces a novel ferromagnetic resonance technique called Ferris FMR for wafer-level measurements and demonstrates the generation of spin currents via the orbital Hall effect in pure copper and aluminum, revealing their potential for spintronic applications.

Contribution

It develops a high-sensitivity, wideband FMR method and experimentally confirms orbital Hall effect-induced spin currents in Cu and Al at wafer scale.

Findings

Cu exhibits a large effective spin Hall angle exceeding Pt.

Al shows an orbital Hall effect of opposite polarity.

The method enables wafer-level spin current measurements.

Abstract

We present a new ferromagnetic resonance (FMR) method that we term the Ferris FMR. It is wideband, has significantly higher sensitivity as compared to conventional FMR systems, and measures the absorption line rather than its derivative. It is based on large-amplitude modulation of the externally applied magnetic field that effectively magnifies signatures of the spin-transfer torque making its measurement possible even at the wafer-level. Using the Ferris FMR, we report on the generation of spin currents from the orbital Hall effect taking place in pure Cu and Al. To this end, we use the spin-orbit coupling of a thin Pt layer introduced at the interface that converts the orbital current to a measurable spin current. While Cu reveals a large effective spin Hall angle exceeding that of Pt, Al possesses an orbital Hall effect of opposite polarity in agreement with the theoretical predictions. Our results demonstrate additional spin- and orbit- functionality for two important metals in the semiconductor industry beyond their primary use as interconnects with all the advantages in power, scaling, and cost.