Test of spin pumping into proximity-polarized Pt by in-phase and out-of-phase pumping in Py/Pt/Py

Spin pumping into proximity-polarized Pt was investigated by magnetic damping studies of Permalloy(Py)/Pt and Py/Pt/Py structures for a Pt thickness range of $0l{d}_{\mathrm{Pt}}l3$ nm. The observed exponential increase in damping with increasing ${d}_{\mathrm{Pt}}$ in Py/Pt is consistent with previous studies of single crystal Fe/Pt. However, at present there are no studies of magnetic double layer structures, ferromagnet/Pt/ferromagnet. The main reason is that the presence of an induced magnetic moment in Pt, by proximity effect, leads to a strong interlayer exchange coupling. Proximity effect has so far not been addressed in the framework of spin pumping. Due to the ferromagnetic interlayer exchange coupling mediated by Pt, the magnetic response of the Py/Pt/Py structure results in optical (out-of-phase) and acoustic (in-phase) resonance modes. The magnetic damping of both modes has a different dependence on ${d}_{\mathrm{Pt}}$ than that of the Py/Pt structure. The study of Py/Pt/Py is sensitive to both the magnitude and phase of spin pumping and thus provides a stringent test of validity for spin-pumping theory for systems with proximity magnetism. We found that the results in Py/Pt and Py/Pt/Py can be self-consistently interpreted by a standard spin pumping theory with ${\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{g}}_{\ensuremath{\uparrow}\ensuremath{\downarrow}}=4.3\ifmmode\times\else\texttimes\fi{}{10}^{15}\ifmmode\pm\else\textpm\fi{}0.4\ifmmode\times\else\texttimes\fi{}{10}^{15}\phantom{\rule{4pt}{0ex}}{\mathrm{cm}}^{\ensuremath{-}2}$ and ${\ensuremath{\lambda}}_{\mathrm{sd}}=1.1\ifmmode\pm\else\textpm\fi{}0.1$ nm. We found no evidence of any additional contributions to the interface damping.