Phase-Sensitive Detection of Spin Pumping via the ac Inverse Spin Hall Effect

We use a phase-sensitive, quantitative technique to separate inductive and ac inverse spin Hall effect (ISHE) voltages observed in Ni81Fe19/normal metal multilayers under the condition of ferromagnetic resonance. For Ni81Fe19/Pt thin film bilayers and at microwave frequencies from 7 to 20 GHz, we observe an ac ISHE magnitude that is much larger than that expected from the dc spin Hall angle Theta(Pt)(SH) = 0.1. Furthermore, at these frequencies, we find an unexpected, approximate to 110 degrees phase of the ac ISHE signal relative to the in-plane component of the resonant magnetization precession. We attribute our findings to a dominant intrinsic ac ISHE in Pt.