Gilbert damping in the layered antiferromagnet CrCl3

We theoretically and experimentally studied the Gilbert damping evolution of both acoustic and optical magnetic resonance modes in the layered flake CrCl₃ with an external magnetic field H applied in plane. Based on a Lagrangian equation and a Rayleigh dissipation function, we predicted that the resonance linewidth ΔH as a function of microwave frequency ω is nonlinear for both acoustic and optical modes in the CrCl₃ flake, which is significantly different from the linear relationship of ΔH ∝ ω in ferromagnets. Measuring the microwave transmission through the CrCl₃ flake, we obtained the ω-H dispersion and damping evolution ΔH-ω for both acoustic and optical modes. Combining both our theoretical prediction and experimental observations, we concluded that the nonlinear damping evolution ΔH-ω is a consequence of the interlayer interaction during the antiferromagnetic resonance, and the interlayer Gilbert dissipation plays an important role in the nonlinear damping evolution because of the asymmetry of the non-collinear magnetizaiton between layers.