Spin pumping and magnetization dynamics in metallic multilayers

TL;DR

This paper investigates how spin pumping influences magnetization dynamics in ferromagnetic/normal-metal multilayers, revealing how interface properties affect damping and confirming findings with experimental data.

Contribution

It provides a theoretical analysis of spin pumping effects on magnetization damping, linking interface conductance to observable damping enhancements and validating with experiments.

Findings

Damping increases with efficient spin relaxation in nonmagnetic layers.

Spin accumulation can oppose spin pumping, reducing damping.

Theoretical predictions agree with experimental measurements.

Abstract

We study the magnetization dynamics in thin ferromagnetic films and small ferromagnetic particles in contact with paramagnetic conductors. A moving magnetization vector causes \textquotedblleft pumping\textquotedblright of spins into adjacent nonmagnetic layers. This spin transfer affects the magnetization dynamics similar to the Landau-Lifshitz-Gilbert phenomenology. The additional Gilbert damping is significant for small ferromagnets, when the nonmagnetic layers efficiently relax the injected spins, but the effect is reduced when a spin accumulation build-up in the normal metal opposes the spin pumping. The damping enhancement is governed by (and, in turn, can be used to measure) the mixing conductance or spin-torque parameter of the ferromagnet--normal-metal interface. Our theoretical findings are confirmed by agreement with recent experiments in a variety of multilayer systems.