  Inelastic scattering of light by spin waves generates an energy flow between
the light and magnetization fields, a process that can be enhanced and
controlled by concentrating the light in magneto-optical resonators. Here, we
model the cooling of a sphere made of a magnetic insulator, such as yttrium
iron garnet (YIG), using a monochromatic laser source. When the magnon
lifetimes are much larger than the optical ones, we can treat the latter as a
Markovian bath for magnons. The steady-state magnons are canonically
distributed with a temperature that is controlled by the light intensity. We
predict that such a cooling process can significantly reduce the temperature of
the magnetic order within current technology.
