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Description
Cavity magnonics studies the coherent interaction between magnons and microwave photons, providing a platform to explore light-matter interaction in magnetic materials [1]. Driving the system into the nonlinear regime unlocks new magnonic phenomena, such as power-dependent frequency shifts [2] and bistability of magnons [3]. Among magnon nonlinearities, the magnon Kerr effect (MKE) appears universally in ferromagnetic systems with finite anisotropy and manifests as a self-induced frequency shift of the magnon modes. We have studied the MKE using a high-quality 200-nm thick yttrium iron garnet film, grown by liquid phase epitaxy, in a strongly coupled magnon–photon system [4]. The cavity is of the loop-gap type, optimized to couple with thin films of magnetic insulators [5]. The MKE is probed as frequency shifts of the magnon–polariton branches when increasing the microwave power, and the cavity serves as a sensitive probe of the magnon dynamics. We investigate the MKE for all orientations of the magnetization with respect to the film plane. The experimental data is well described by a newly derived theoretical model of the MKE in a thin ferromagnetic film [6]. Our study predicts the trade-off between anharmonicity of a magnonic system and the threshold for coherent magnon–photon coupling, which is necessary to probe the magnetization dynamics.
[1] Rameshti, B. Z., et al., Physics Reports 979, 1-61 (2022).
[2] Wang, Y.P., et al., Physical Review B 94, 224410 (2016).
[3] Wang, Y.P., et al., Physical Review Letters 120, 057202 (2018).
[4] DP., et al. "Magnon Kerr effect in a ferrimagnetic thin film strongly coupled to a microwave resonator." In review.
[5] Zanichelli, F., DP., et al. "Loop-gap resonators achieving strong magnon–photon coupling in magnetic insulator thin films." Accepted.
[6] DP., et al. "Model of the magnon Kerr effect in a highly anisotropic ferromagnet." In preparation.