Observation of magnon-mediated current drag in Pt/yttrium iron garnet/Pt(Ta) trilayers

TLDR

Pure spin currents can be generated either by the spin Hall effect in heavy metals such as Pt or Ta, or by magnon excitations in magnetic insulators like yttrium iron garnet. We show that in NM/MI/NM trilayers the spin Hall and magnonic spin currents are interconvertible via a magnon‑mediated current drag, with a linear dependence on driving current and a power‑law exponent between 1.5 and 2.5, indicating the trilayer can function as a scalable pure spin current valve.

Abstract

Pure spin current, a flow of spin angular momentum without flow of any companying net charge, is generated in two common ways. One makes use of the spin Hall effect in normal metals (NM) with strong spin-orbit coupling, such as Pt or Ta. The other utilizes the collective motion of magnetic moments or spin waves with the quasi-particle excitations called magnons. A popular material for the latter is yttrium iron garnet, a magnetic insulator (MI). Here we demonstrate in NM/MI/NM trilayers that these two types of spin currents are interconvertible across the interfaces, predicated as the magnon-mediated current drag phenomenon. The transmitted signal scales linearly with the driving current without a threshold and follows the power-law with n ranging from 1.5 to 2.5. Our results indicate that the NM/MI/NM trilayer structure can serve as a scalable pure spin current valve device which is an essential ingredient in spintronics.