Spin pumping in strongly coupled magnon-photon systems

TL;DR

This paper experimentally investigates magnon-polaritons in a ferrimagnetic resonance system within a microwave cavity, demonstrating tunable strong coupling and analyzing multiple spin wave modes' interactions with the cavity.

Contribution

It provides the first experimental demonstration of tunable strong magnon-photon coupling and detailed analysis of multiple spin wave modes in a cavity system.

Findings

Strong coupling regime can be tuned by cavity decay rate adjustments.

Magnon-photon coupling and spin pumping signals are quantitatively characterized.

Multiple spin wave modes exhibit measurable coupling to the cavity.

Abstract

We experimentally investigate magnon-polaritons, arising in ferrimagnetic resonance experiments in a microwave cavity with a tuneable quality factor. To his end, we simultaneously measure the electrically detected spin pumping signal and microwave reflection (the ferrimagnetic resonance signal) of a yttrium iron garnet (YIG) / platinum (Pt) bilayer in the microwave cavity. The coupling strength of the fundamental magnetic resonance mode and the cavity is determined from the microwave reflection data. All features of the magnetic resonance spectra predicted by first principle calculations and an input-output formalism agree with our experimental observations. By changing the decay rate of the cavity at constant magnon-photon coupling rate, we experimentally tune in and out of the strong coupling regime and successfully model the corresponding change of the spin pumping signal. Furthermore, we observe the coupling and spin pumping of several spin wave modes and provide a quantitative analysis of their coupling rates to the cavity.