  We studied the spin injection in a NiFe(Py)/Si system using broadband
ferromagnetic resonance spectroscopy. The Gilbert damping parameter of the Py
layer on top of the Si channel was determined as a function of the Si doping
concentration and Py layer thickness. For fixed Py thickness we observed an
increase of the Gilbert damping parameter with decreasing resistivity of the Si
channel. For a fixed Si doping concentration we measured an increasing Gilbert
damping parameter for decreasing Py layer thickness. No increase of the Gilbert
damping parameter was found Py/Si samples with an insulating interlayer. We
attribute our observations to an enhanced spin injection into the
low-resistivity Si by spin pumping.
