Fig. 2: Ferrimagnetic resonance linewidth in yttrium-iron-garnet (YIG) at ν = 104 GHz frequency.

Resonance curves show the γαω intrinsic damping in the imaginary part of the magnetic permeability (\({\rm{Im}}(\mu )\), green, on the inverse scale of the right axis) together with the observed transmission in the Faraday (magnetic field parallel to light propagation direction, red open diamonds) and Voigt (magnetic field perpendicular to light propagation direction, red filled diamonds) geometries. In the latter cases, the further line broadening is attributed to the radiative damping, \({{{\Gamma }}}_{{\rm{rad}}}^{{\rm{V}}}\). γ, α, and ω stand for the gyromagnetic ratio, the dimensionless intrinsic damping rate, and the angular frequency, respectively. The horizontal axis shows the magnetic field H relative to the corresponding resonance field H₀. Labels on the left vertical axis belong to the experimental curves and indicate the transmitted light intensity I relative to the gadolinium-gallium-garnet (GGG) substrate’s transmission baseline I_GGG, which can be measured without the YIG layer. The frequency dependences of the ferrimagnetic resonance fields (open/filled symbols for Faraday/Voigt geometry experiments) in two YIG films of different thicknesses (blue squares for d = 3 μm and red diamonds for d = 6.1 μm) are presented in the inset, where dashed/solid lines show theoretical expectations of the resonance frequencies for Faraday/Voigt geometry. On the scale of the inset, symbols corresponding to the two samples at a given frequency are completely superposed and are bigger than the corresponding error bars.