Magnon Kerr Effect in a Magnetic Thin Film Strongly Coupled to a Microwave Resonator

Progress in cavity magnonics relies on tunable nonlinearities in magnon-photon interactions for controlling magnon dynamics and frequency conversion. Here, we demonstrate the magnon Kerr effect in anisotropic magnonic systems comprising iron garnet thin films coupled to a loop-gap microwave resonator. The strong shape anisotropy, combined with strain, enhances the magnon Kerr effect compared to a sphere of equivalent volume by up to 3 orders of magnitude, while the cavity enables sensitive probing of magnetization dynamics. We demonstrate continuous tunability of the magnitude and sign of the Kerr shift by controlling the static orientation of the magnetization, in excellent agreement with theory. Our findings demonstrate a scalable approach to enhancing Kerr anharmonicity in hybrid magnon-photon systems while preserving coherent magnon-photon interactions.