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

TL;DR

This study examines how spin pumping damping varies with Pd and Pt layer thicknesses in ferromagnetic junctions, revealing different behaviors depending on contact type and the presence of induced magnetic moments.

Contribution

It demonstrates the thickness-dependent damping behavior and the role of induced moments in Pd and Pt, providing new insights into spin current scattering mechanisms.

Findings

Linear damping dependence in direct contact junctions.

Exponential damping dependence when separated by Cu.

Induced magnetic moments in Pd and Pt near interfaces.

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$_\textrm{N}$ 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.