Identification of orbital pumping from spin pumping and rectification effects

TL;DR

This paper demonstrates experimental methods to distinguish orbital pumping from spin pumping and rectification effects in bilayer structures, advancing the understanding of pure orbital current generation from ferromagnets.

Contribution

It introduces techniques to separate orbital pumping signals from spin-related effects by analyzing voltage angular and spatial dependencies.

Findings

Sign reversal of voltage indicates orbital pumping presence.

Distinct angular dependence differentiates orbital from spin effects.

Spatial analysis helps isolate orbital pumping signals.

Abstract

The recently predicted mechanism of orbital pumping enables the generation of pure orbital current from a precessing ferromagnet (FM) without the need for electrical current injection. This orbital current can be efficiently injected into an adjacent nonmagnetic material (NM) without being hampered by electrical conductivity mismatch. However, experimentally identifying this novel effect presents significant challenges due to the substantial background contributions from spin pumping and spin rectification effects (SREs). In this work, we disentangle the effects of orbital pumping from spin pumping in bilayer structures composed of Nb/Ni and Nb/$\mathrm{Fe_{60}Co_{20}B_{20}}$ by observing a sign reversal of the measured voltage. This reversal arises from the competing signs of the spin and orbital Hall effects in the Nb. We establish methods to differentiate the pumping signal from SREs by analyzing the distinct angular dependence of the measured voltage and its spatial dependence relative to the radio frequency excitation source.