Influence of Ferromagnetic Film Thickness on Acoustically Driven Spin Wave Resonances

We consider the spin wave resonances (SWRs) magnetoelastic excitation and electric detection in a hybrid bulk acoustic wave resonator containing YIG/Pt bilayer. The influence of micrometer and submicrometer yttrium iron garnet (YIG) film thickness on the efficiency of SWR excitation accompanied by a spin pumping from YIG to Pt has been theoretically studied. The frequency and thickness dependencies of inverse spin Hall effect (ISHE) voltage and microwave reflection coefficient are analytically and numerically investigated and discussed. Due to the non-uniform effective magnetic field of elastic nature, the higher SWR modes (both even and odd) can be excited with an efficiency comparable to the efficiency of the fundamental mode at the ferromagnetic resonance frequency. If an integer number of acoustic half-waves fits into the YIG film thickness, forbidden zones arise in the SWR spectrum: at certain thickness values, only even or only odd SWR modes are excited.