Minor typo. Paper:

>17.5% of the measured value for Terbium-Gallium-Garnet (TGG) at 800 nm [NIR], and up to 75% at 1.3 µm.

Note there's almost no effect on transmission, which may explain why nobody noticed until now..

transmission plot (UV-IR)

https://www.samaterials.com/terbium-gallium-garnet-crystal.h...

What it looks like IRL

https://www.photonchinaa.com/tgg-terbium-gallium-garnet/

Relevant? Intrinsic Gilbert damping (2009) https://dspace.mit.edu/handle/1721.1/51819