Polycrystalline YIG Thin Films on a Piezoelectric Substrate for Magnetoacoustic Hybrid Devices

Today's widespread research on future magnonic devices is often based on garnet thin films due to their insulating nature and ultralow Gilbert damping. Moreover, surface acoustic waves (SAWs) are frequently used in microwave devices, and therefore, exploiting the interaction between SAWs and spin waves in magnetoacoustic hybrid devices is a promising research field. We have grown a polycrystalline yttrium iron garnet (YIG) thin film on a commonly used piezoelectric substrate (LiNbO₃), combining SAW technology with an insulating garnet thin film. Crystallization of the garnet is achieved through precise adjustment of pulsed laser deposition (PLD) and postannealing parameters. The resulting polycrystalline YIG film exhibits an in-plane uniaxial magnetic anisotropy, attributed to anisotropic strain caused by mismatched anisotropic thermal expansion coefficients of the substrate and film. It show a Gilbert damping of 0.002 to 0.005, comparable to polycrystalline YIG films prepared on (oxidized) silicon substrates. Additionally, SAW transmission measurements reveal strong nonreciprocal magnetoacoustic coupling with a maximum attenuation of 1.4 dB/mm, which is described by a phenomenological model.