# Magnon mode selective spin transport in compensated ferrimagnets

## TL;DR

This study explores how magnonic thermal spin currents are generated and transported in compensated ferrimagnet/metal bilayers, revealing mode selectivity and interface effects that influence the spin Seebeck effect's temperature dependence.

## Contribution

It demonstrates the universality of complex temperature dependence in the spin Seebeck effect and highlights the dominant role of interface effects in mode selective spin transport.

## Key findings

- Non-monotonic temperature dependence of spin Seebeck signals with sign changes.
- Interface effects significantly modify the magnitude and temperature dependence of the signals.
- Mode selective interface transmission probabilities depend on material combinations.

## Abstract

We investigate the generation of magnonic thermal spin currents and their mode selective spin transport across interfaces in insulating, compensated ferrimagnet/normal metal bilayer systems. The spin Seebeck effect signal exhibits a non-monotonic temperature dependence with two sign changes of the detected voltage signals. Using different ferrimagnetic garnets, we demonstrate the universality of the observed complex temperature dependence of the spin Seebeck effect. To understand its origin, we systematically vary the interface between the ferrimagnetic garnet and the metallic layer, and by using different metal layers we establish that interface effects play a dominating role. They do not only modify the magnitude of the spin Seebeck effect signal but in particular also alter its temperature dependence. By varying the temperature, we can select the dominating magnon mode and we analyze our results to reveal the mode selective interface transmission probabilities for different magnon modes and interfaces. The comparison of selected systems reveals semi-quantitative details of the interfacial coupling depending on the materials involved, supported by the obtained field dependence of the signal.