Spin pumping damping and magnetic proximity effect in Pd and Pt spin-sink layers

Abstract

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${}_{\text{N}}$ 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.