Spin pumping in NbRe/Co superconductor-ferromagnet heterostructures

Ferromagnetic resonance (FMR) spectroscopy measurements were performed on NbRe/Co/NbRe trilayers in order to probe spin pumping across the superconductor/ferromagnet interface and to detect the possible presence of spin-triplet pairing in the superconducting NbRe layer. FMR spectra were acquired as a function of frequency, magnetic field, and temperature, and reveal that the Gilbert damping parameter associated with spin pumping remains almost constant as temperature goes down through the superconducting transition. Additionally, the dependence of the Gilbert damping parameter on the thickness of the NbRe layer in trilayers is used to determine the values of the spin mixing conductance at the interface (18 - 21 nm(-2)) and the spin diffusion length (7.1 - 12.5 nm) in the NbRe layer. These findings may suggest that spin pumping would still be effective even though NbRe becomes superconducting, which would indicate that the spin-triplet would be the dominant pairing mechanism. Future experiments are proposed in light of these results.