Photonic crystal cavities based on suspended yttrium iron garnet nanobeams

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 Ω/ 2πapprox 1.52 GHz and a backward-volume spin-wave mode at Ω/ 2π= 11.59 GHz under an in-plane bias field. Although we measure only the photonic resonance intrinsic $Q sim 2 times 10³$ in this study, the device lays the groundwork for future exploration of coupled photon-phonon-magnon dynamics once higher optical quality factors are achieved.