  We measure electrically detected ferromagnetic resonance in microdevices
patterned from ultra-thin Co/Pt bilayers. Spin pumping and rectification
voltages are observed and distinguished via their angular dependence. The
spin-pumping voltage shows an unexpected increase as the cobalt thickness is
reduced below 2 nm. This enhancement allows more efficient conversion of spin
to charge current and motivates a theory modelling the dependence of impurity
scattering on surface roughness.
