Temperature dependence of the magnon–phonon coupling in yttrium iron garnet/gadolinium gallium garnet high overtone bulk acoustic resonators

We experimentally study the temperature dependence of the magnon–phonon coupling in a yttrium iron garnet (YIG)/gadolinium gallium garnet (GGG) heterostructure. More specifically, we use broadband ferromagnetic resonance to investigate the magneto-elastic coupling between the Kittel mode of a YIG thin film and the transverse acoustic phonon modes of the YIG/GGG high overtone bulk acoustic wave acoustic resonator for in and out-of-plane field directions in the temperature range between T = 5 and 300 K. We find that for a magnetic field applied normal to the film surface, magneto-elastic coupling decreases with decreasing temperature, whereas it increases for the in-plane magnetic field configuration. The observed temperature dependence differs from earlier observations on bulk YIG samples, which might be due to the temperature dependent stress imposed by the GGG substrate. We also present the temperature dependence of the stiffness tensor element C44 for GGG between 5 K and room temperature.