Exceptional sign changes of the non-local spin Seebeck effect in antiferromagnetic hematite

TL;DR

This paper investigates the long-distance transport of thermally generated magnonic spin currents in antiferromagnetic hematite, revealing exceptional sign changes in the non-local spin Seebeck effect and demonstrating significant thermal spin transport without net magnetization.

Contribution

It provides experimental and theoretical insights into magnonic spin current transport in hematite, highlighting the role of magnetic order parameters and sign changes in the non-local spin Seebeck effect.

Findings

Significant thermal spin transport observed without net magnetization

Magnon transport occurs both parallel and perpendicular to the easy-axis

Significant sign changes in the non-local spin Seebeck effect

Abstract

Low power spintronic devices based on the propagation of pure magnonic spin currents in antiferromagnetic insulator materials offer several distinct advantages over ferromagnetic components including higher frequency magnons and a stability against disturbing external magnetic fields. In this work, we make use of the insulating antiferromagnetic phase of iron oxide, the mineral hematite $\alpha$-Fe$_2$O$_3$ to investigate the long distance transport of thermally generated magnonic spin currents. We report on the excitation of magnons generated by the spin Seebeck effect, transported both parallel and perpendicular to the antiferromagnetic easy-axis under an applied magnetic field. Making use of an atomistic hematite toy model, we calculate the transport characteristics from the deviation of the antiferromagnetic ordering from equilibrium under an applied field. We resolve the role of the magnetic order parameters in the transport, and experimentally we find significant thermal spin transport without the need for a net magnetization.