Orbital Pumping in Ferrimagnetic Insulators

TL;DR

This paper demonstrates the generation and detection of pure orbital currents in Bi-doped yttrium iron garnet, revealing the role of orbital magnetization dynamics and interface transparency in orbital pumping efficiency.

Contribution

It provides the first experimental evidence of orbital current pumping in magnetic insulators and distinguishes it from spin current contributions.

Findings

Orbital currents are generated by orbital magnetization dynamics in BiYIG.

Orbital pumping efficiency is enhanced by better interfacial transparency.

Orbital currents are a minority compared to spin currents in the total angular momentum pumped.

Abstract

We report the detection of pure orbital currents generated by both coherent and thermal magnons in the magnetic insulator Bi-doped yttrium iron garnet (BiYIG). The pumping of orbital and spin currents is jointly investigated in nano-devices made of naturally oxidized Cu, pure Cu, Pt, and Cr. The absence of charge conduction in BiYIG and the negligible spin-to-charge conversion of oxidized Cu allows us to disambiguate the orbital current contribution. Comparative measurements on YIG and BiYIG show that the origin of the orbital pumping in BiYIG/oxidized Cu is the dynamics of the orbital magnetization in the magnetic insulator. In Cr, the pumping signal is dominated by the negative spin Hall effect rather than the positive orbital Hall effect, indicating that orbital currents represent a minority of the total angular momentum current pumped from the magnetic insulator. Our results also evidence that improving the interfacial transparency significantly enhances pumping efficiencies not only for spin, but also for orbital currents.