Effective spin-mixing conductance of heavy-metal-ferromagnet interfaces

TL;DR

This paper critically examines the methods for measuring the effective spin-mixing conductance at heavy-metal-ferromagnet interfaces, revealing that common assumptions lead to significant inaccuracies due to overlooked damping mechanisms.

Contribution

It demonstrates that two-magnon scattering and spin-memory-loss effects dominate damping, challenging the traditional assumption that spin pumping is the primary mechanism.

Findings

Neglecting two-magnon scattering causes overestimation of G_eff.

Spin-memory-loss significantly affects damping measurements.

Correcting for these effects yields more accurate spin Hall parameters.

Abstract

The effective spin-mixing conductance (G_eff) of a heavy metal/ferromagnet (HM/FM) interface characterizes the efficiency of the interfacial spin transport.Accurately determining G_eff is critical to the quantitative understanding of measurements of direct and inverse spin Hall effects. G_eff is typically ascertained from the inverse dependence of magnetic damping on the FM thickness under the assumption that spin pumping is the dominant mechanism affecting this dependence.Here we report that, this assumption fails badly in many in-plane magnetized prototypical HM/FM systems in the nm-scale thickness regime. Instead, the majority of the damping is from two-magnon scattering at the FM interface, while spin-memory-loss scattering at the interface can also be significant.If these two effects are neglected, the results will be an unphysical "giant" apparent G_eff and hence considerable underestimation of both the spin Hall ratio and the spin Hall conductivity in inverse/direct spin Hall experiments.