Ferromagnetic resonance in superconductor/ferromagnet bilayers*

We experimentally investigate broadband ferromagnetic resonance (FMR) in bilayers that combine the high-temperature superconductor YBa$_{\mathrm{2}}$Cu$_{\mathrm{3}}$O$_{\mathrm{7}}$ with different ferromagnets, either Permalloy or the half-metallic La$_{\mathrm{1-x}}$Ca$_{\mathrm{x}}$MnO$_{\mathrm{3}}$. The observed behavior is compared to that of reference ferromagnetic layers. In bilayers, the FMR signal contains contributions from both the superconducting and ferromagnetic layers. The FMR linewidth is studied as a function of temperature (2K-200K) and frequency (up to 20 GHz) to obtain the damping constant above and below the superconducting critical temperature. The results will be discussed in the frame of the spin-pumping theory considering the superconductor a spin sink where part of the FMR generated angular momentum relaxes in the superconductor martial trough spin-pumpin [1]. [1] Yokoyama, T. {\&} Tserkovnyak, Y. Tuning odd triplet superconductivity by spin-pumping. Phys. Rev. B 80, 104416 (2009)