Spin injection into silicon detected by broadband ferromagnetic resonance spectroscopy

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 a fixed Py thickness, we observed an increase in 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 in the Gilbert damping parameter was found for Py/Si samples with an insulating interlayer. We attribute our observations to an enhanced spin injection into the low-resistivity Si by spin pumping.