Extended Data Fig. 4: Phonon spectra of GGG.

Imaginary parts of the dielectric function ε(ω) (black) and the loss function -1/ε(ω) (blue) for Gd₃Ga₅O₁₂. The shaded background shows the infrared transmission spectrum of 7.3 μm thick YIG:Co. The 15% to 20% transparency region around the LO mode at 490 cm⁻¹ is marked by the dotted lines in Extended Data Figs. 3 and 5.