Observation of room temperature exchange cavity magnon‐polaritons in metallic thin films

Cavity magnonics has become an intriguing field due to its potential to enable next‐generation technologies centered around controlling information exchange in hybrid resonant systems. Investigating the tunability of magnon‐photon coupling is key to advancing the field. Here, the observation of coupling between the first order magnon mode in a metallic thin film with a cavity photon mode is reported. An electromagnetic perturbation theory that takes account of perpendicular standing spin waves and their respective dissipation is utilized to estimate the coupling strength. The metallic thin film exhibits notably lower dissipation for the higher‐order magnon mode, which is not observed in a thin film magnetic insulator. As such, and given that metallic Kittel magnons typically exhibit lower coherence times than their insulator counterparts, the excitation and coupling to specific higher order modes could lengthen these times compared to previous observations, which may be useful for future integration into quantum devices.