Magnons versus electrons in thermal spin transport through metallic interfaces

TL;DR

This paper presents a unified theory for spin transport in magnetic metals, highlighting how magnons and electrons contribute to thermally-driven spin injection, with magnonic effects potentially dominating at typical temperatures.

Contribution

It introduces a model that treats magnonic and electronic contributions equally and derives how their ratio depends on temperature and material properties.

Findings

Magnonic contribution can dominate thermal spin injection.

The ratio of magnonic to electronic contribution scales as /T_C.

Magnonic effects are significant even with transparent electronic interfaces.

Abstract

We develop a theory for spin transport in magnetic metals that treats the contribution of magnons and electrons on equal footing. As an application we consider thermally-driven spin injection across an interface between a magnetic metal and a normal metal, i.e., the spin-dependent Seebeck effect. We show that the ratio between magnonic and electronic contribution scales as $\sqrt{T/T_C}T_F/T_C$, with the Fermi temperature $T_F$ and the Curie temperature $T_C$. Since, typically, $T_C \ll T_F$, the magnonic contribution may dominate the thermal spin injection, even though the interface is more transparent for electronic spin current.