We report the fabrication and optical characterization of an air-suspended photonic crystal nanobeam cavity in yttrium iron garnet (YIG) realized by focused-ion-beam milling. YIG’s combination of low optical loss and ferrimagnetism makes it highly attractive for quantum technologies, yet prior work has largely been focused on millimeter-scale spheres and simple microstructures, hindering true on-chip integration. Demonstrating nanometer-scale patterning in a suspended geometry therefore represents an important advance. Finite-element simulations predict that the same structure supports a flapping-type mechanical mode at ${\mathrm{\Omega }}_m/2\pi \approx 1.52\mathrm{GHz}$ and a backward-volume spin-wave mode at ${\omega }_{\mathrm{mag}}/2\pi =11.59\mathrm{GHz}$ under an in-plane bias field. Although we measured only the photonic resonance (intrinsic $Q\approx 2\times {10}^3$) in this study, the device lays the groundwork for future exploration of coupled photon-phonon-magnon dynamics once higher optical quality factors are achieved.

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• Light-matter interaction
• Optomechanics
• Quantum information with hybrid systems
• Magnetic insulators
• Magnonic crystals
• Micromechanical & nanomechanical oscillators
• Optical microcavities
• Phononic crystals