# Non-Reciprocal Spin Pumping in Asymmetric Magnetic Trilayers

## TL;DR

This paper develops a new theory for spin pumping in magnetic trilayers with different interfaces, revealing non-reciprocal behavior and significant differences in damping, impacting spintronic device dynamics.

## Contribution

The paper introduces a general theory for spin pumping in systems with multiple distinct interfaces, challenging the reciprocal assumption.

## Key findings

- Spin pumping is non-reciprocal in asymmetric trilayers.
- Large differences in interface damping were observed.
- Layer-resolved FMR experiments confirmed theoretical predictions.

## Abstract

In magnetic trilayer systems, spin pumping is generally addressed as a reciprocal mechanism characterized by one unique spin mixing conductance common to both interfaces. However, this assumption is questionable in cases where different types of interfaces are present in the material. Here, we present a general theory for analyzing spin pumping in cases with more than one unique interface. The theory is applied to analyze layer-resolved ferromagnetic resonance experiments on the trilayer system Ni$_{20}$Fe$_{80}$/Ru/Fe$_{49}$Co$_{49}$V$_2$ where the Ru spacer thickness is varied to tune the indirect exchange coupling. The results show that the spin pumping in trilayer systems with dissimilar magnetic layers is non-reciprocal, with a surprisingly large difference between spin-pumping induced damping of different interfaces. Our findings have importance on dynamics of spintronic devices based on magnetic multilayer materials.