We report the observation of the Purcell effect in a cavity-metallic-magnet hybrid system using electric field mediated coupling. In this configuration, microwave-induced axial currents in the microwire induce circular magnetic fields that drive the ferromagnetic resonance (FMR) of the magnetized microwire. Field-dependent transmission and reflection spectroscopies reveal a clear cavity perturbation consistent with the Purcell regime, in which the magnetic loss rate exceeds the light-matter coupling strength. Despite the small magnetic volume ($\sim {10}^{-13}{\text{m}}^3$), measurements performed at both room temperature and $T=7\mathrm{m}\mathrm{K}$ show coupling rates as high as $g/2\pi =56\mathrm{M}\mathrm{Hz}$, one order of magnitude stronger than the one expected from conventional coupling at the magnetic antinode. Time-domain ringdown measurements directly show the magnetic field-dependent modification of the cavity photon lifetime, in agreement with theoretical predictions. These results establish a versatile approach for coupling microwave fields to metallic magnets via geometric and electric field mediated interactions, opening new opportunities for hybrid cavity-magnet systems.

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• Cavity quantum electrodynamics
• Magnetism
• Magnons
• Ferromagnetic resonance