We investigated the spin pumping damping contributed by paramagnetic layers (Pd, Pt) in both direct and indirect contact with ferromagnetic Ni$_{ 81}$Fe$_{ 19}$ films. We find a nearly linear dependence of the interface-related Gilbert damping enhancement $\Delta\alpha$ on the heavy-metal spin-sink layer thicknesses t$_\textrm{ N}$ in direct-contact Ni$_{ 81}$Fe$_{ 19}$/(Pd, Pt) junctions, whereas an exponential dependence is observed when Ni$_{ 81}$Fe$_{ 19}$ and (Pd, Pt) are separated by \unit[3]{ nm} Cu. We attribute the quasi-linear thickness dependence to the presence of induced moments in Pt, Pd near the interface with Ni$_{ 81}$Fe$_{ 19}$, quantified using X-ray magnetic circular dichroism (XMCD) measurements. Our results show that the scattering of pure spin current is configuration-dependent in these systems and cannot be described by a single characteristic length.
Categories: cond-mat.mes-hall