Loop-gap resonators achieving strong magnon-photon coupling in magnetic insulator thin films

TL;DR

This paper introduces a modular loop-gap resonator that effectively couples with thin magnetic insulator films, enabling strong magnon-photon interactions and advanced spectroscopic techniques at room temperature.

Contribution

The study presents a novel loop-gap resonator design optimized for thin magnetic insulator films, demonstrating strong coupling and new spectroscopic capabilities in cavity magnonics.

Findings

Achieved strong magnon-photon coupling with a 75 nm yttrium iron garnet film.

Implemented field-differential spectroscopy to isolate hybrid system signals.

Enabled hybridization with standing spin-wave modes across the film thickness.

Abstract

Magnon-photon hybrid systems consisting of a three-dimensional electromagnetic resonator and a bulk magnetic insulator constitute the standard experimental platform in cavity magnonics. Here, we demonstrate a modular loop-gap resonator design optimized to couple with thin films of magnetic insulators. We achieve the strong-coupling regime using this loop-gap resonator coupled to a 75~nm-thick epitaxial film of yttrium iron garnet at room temperature. We further show how to perform field-differential spectroscopy of the hybrid magnon-photon system, which eliminates the unwanted signal from other loop-gap modes uncoupled to the magnetic film. In addition to the uniform ferromagnetic resonance mode, the loop-gap resonator enables an hybridization with the standing spin-wave modes forming across the thickness of the film. Our approach unlocks the use of epitaxial films and multilayers of magnetic insulators to tune the magnon band structure in cavity magnonics experiments.