Effect of direct exchange on spin current scattering in Pd and Pt

We show evidence for a magnetic proximity effect on spin current scattering in Pt and Pd. The return loss of pumped spin current, measured through the interface-related Gilbert damping $\Delta\alpha$, is found to be linear in thickness for Pd and Pt in contact with Ni$_{81}$Fe$_{19}$, but exponential in thickness for the same layers separated from Ni$_{81}$Fe$_{19}$ by Cu(3nm). The linear onset is attributed to ferromagnetic order in Pd and Pt, verified through x-ray magnetic circular dichroism (XMCD) measurements. The measurements show that the scattering of pure spin current is configuration-dependent in these paramagnets and not described by a single characteristic length.