Microwave control of thermal magnon spin transport

TL;DR

This study demonstrates that microwave fields can significantly modulate thermal magnon transport in yttrium iron garnet, revealing both suppression at resonance and enhancement at non-resonant conditions related to magnon band minima.

Contribution

It uncovers how rf microwave fields influence incoherent thermal magnon transport, highlighting effects beyond ferromagnetic resonance and involving magnon band-minimum states.

Findings

Ferromagnetic resonance suppresses magnon transport by 95%.

Non-resonant enhancement of magnon signals up to 800%.

Modulation linked to magnon band minima and chiral surface modes.

Abstract

We observe that an rf microwave field strongly influences the transport of incoherent thermal magnons in yttrium iron garnet. Ferromagnetic resonance in the nonlinear regime suppresses thermal magnon transport by 95%. The transport is also modulated at non-resonant conditions in two cases, both related to the magnon band minimum. Firstly, a strong enhancement of the nonlocal signal appears at a static magnetic field below the resonance condition. This increase only occurs at one field polarity and can be as large as 800%. We attribute this effect to magnon kinetic processes, which give rise to band-minimum magnons and high-energy chiral surface modes. Secondly, the signal increases at a static field above the resonance condition, where the rf frequency coincides with the magnon band minimum. Our study gives insight into the interplay between coherent and incoherent spin dynamics: The rf field modifies the occupation of relevant magnon states and, via kinetic processes, the magnon spin transport.