Magnetization coupling in a YIG/GGG structure

We studied the magnetization coupling between an yttrium-iron-garnet (YIG) film and a gadolinium-gallium-garnet (GGG) substrate at low temperature using magnetic resonance measurements. We observed both acoustic and optical mode hybridization between the magnetization of the 3-$\ensuremath{\mu}\text{m-thick}$ YIG film, ${M}_{\mathrm{YIG}}$, and the magnetization of the GGG substrate, ${M}_{\mathrm{GGG}}$, corresponding to in-phase and out-of-phase coupling, respectively. This experimental observation can be described by an antiferromagnetic-type interaction between ${M}_{\mathrm{YIG}}$ and ${M}_{\mathrm{GGG}}$ in the Landau-Lifshitz-Gilbert equation. Taking this approach we find that the effective field induced by magnetization coupling can be enhanced by decreasing the temperature or increasing the external field, providing a means to control magnon dynamics in YIG for magnonic device applications.