Magnon Kerr effect in a magnetic thin film strongly coupled to a microwave resonator

Abstract

Cavity magnonics investigates hybrid systems where magnons interact coherently with photons, providing a platform to harness light-matter interaction in magnetic materials. Progress in this field hinges on achieving stronger and tunable nonlinear effects, which are essential for controlling magnon dynamics and frequency conversion. Here, we demonstrate the magnon Kerr effect in an anisotropic magnonic system comprising a 200~nm-thick yttrium iron garnet film strongly coupled to a three-dimensional microwave resonator. The strong shape anisotropy significantly enhances the magnon Kerr effect compared to a sphere of equivalent volume, 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. Input-output modeling of the magnon-photon interaction provides a consistent description of our system and Kerr coefficients matching the experimental results. Our findings demonstrate a scalable approach to enhancing Kerr anharmonicity in hybrid magnon-photon systems while preserving strong coupling.

Figures (5)

• Figure 1: (a) Experimental setup showing the sample and microwave resonator placed in an electromagnet and connected to the VNA. The microwave signal is amplified by net $15dB$. The resonator can be rotated to change the relative angle between the applied magnetic field and the sample plane. (b) Photograph of the resonator linkPRR, with probing antennas and the YIG film in the sample space. (c) Schematic of field angle $\theta_\mathrm{H}$ and magnetization angle $\theta_\mathrm{M}$ with respect to the normal to the (111)-oriented YIG film.
• Figure 2: Field- and frequency-dependent microwave transmission of the coupled magnon–photon system: measured in the IP configuration at (a) $P=-5dBm$ and (c) $P = 25dBm$, and in the OOP configuration at (b) $P=-5dBm$ and (d) $P = 25dBm$. Dashed lines follow the maximas in the transmission and mark the magnon–polariton branches at $P=-5dBm$ (white) and at $P=25dBm$ (red), and arrows indicate the shift direction. The OOP upper magnon–-polariton branch at $P = 25dBm$ does not appear due to foldover.
• Figure 3: Power- and frequency-dependent microwave transmission measurements, and fits for the coupled magnon-photon system at a fixed field near the center of the avoided crossing. Field angle is (a,d) $\theta_\mathrm{H}=90°$, (b,e) $\theta_\mathrm{H}=0°$, and (c,f) $\theta_\mathrm{H}=40°$, for (a,b,c) measurements and (d,e,f) fits.
• Figure 4: (a) Dependence of magnetization angle $\theta_\mathrm{M}$ on field angle $\theta_\mathrm{H}$, (b) Kerr coefficient $\mathcal{K}/(2\pi)$, (c) magnon dissipation rate $\kappa_\mathrm{m}/(2\pi)$, and (d) anharmonicity defined as $\mathcal{K}/\kappa_\mathrm{m}$, all as functions of $\theta_\mathrm{M}$.
• Figure 5: Experimental observations (filled markers) and extrapolated values based on previous works PhysRevB.94.224410PhysRevLett.120.057202PhysRevLett.129.123601Shen2025PhysRevLett.123.107701PhysRevLett.123.107702Guo2023zw18-26nw (empty markers) for (a) $|\mathcal{K}|/\kappa_\mathrm{m}$ versus magnetic volume for spheres and films and (b) anharmonicity $|\mathcal{K}|/\kappa_\mathrm{m}$ versus $g/\kappa_\mathrm{m}$. The shaded region for spheres in (a) represents attainable values of $|\mathcal{K}|/\kappa_\mathrm{m}$ calculated for YIG, with $\kappa_\mathrm{m}/(2\pi)$ ranging 0.5--25MHz. For films, the shaded region is both for IP and OOP fields, calculated for YIG and permalloy at $f=10GHz$, with $\kappa_\mathrm{m}/(2\pi)$ ranging 0.5--500MHz. We used $M_\mathrm{s}=796kA.m^{-1}$ for permalloy PhysRevLett.123.107701.