  Spin pumping is a recently established means for generating a pure spin
current, whereby spins are pumped from a magnet into the adjacent target
material under the ferromagnetic resonance condition. We theoretically
investigate the spin pumping from an insulating ferromagnet into spin glass
materials. Combining a dynamic theory of spin glasses with the linear-response
formulation of the spin pumping, we calculate temperature dependence of the
spin pumping near the spin glass transition. The analysis predicts that a
characteristic peak appears in the spin pumping signal, reflecting that the
spin fluctuations slow down upon the onset of spin freezing.
