Magnon diffusion lengths in bulk and thin film Fe3O4 for spin Seebeck applications

G Venkat,M D Cropper,K Morrison,C D W Cox,A Piovano,D Voneshen,A J Caruana

doi:10.1103/physrevmaterials.4.075402

Abstract

The determination of the magnon diffusion length (MDL) is important for increasing the efficiency of spin Seebeck effect (SSE) based devices utilising non-metallic magnets. We extract the MDL at $50$ and $300\,\rm{K}$ in an $\rm{Fe}_{3}\rm{O}_{4}$ single crystal from the magnon dispersion obtained using inelastic neutron scattering (INS) and find them to be equal within error. We then measure the heat flux normalised SSE responses and in-plane magnetization of $\rm{Fe}_{3}\rm{O}_{4}$ thin films and normalise by the static magnetization contribution to the SSE before determining the MDLs from a fit of the thickness dependence. We find that the MDLs determined in this way are smaller than that measured from INS which maybe due to differences in magnon propagation between bulk and thin film $\rm{Fe}_{3}\rm{O}_{4}$.

Highlights

The spin Seebeck effect (SSE) was demonstrated in 2008 by Uchida et al and has since sparked a lot of interest for potential thermoelectric applications [1]
The SSE was initially demonstrated in a metallic ferromagnet [1], it was later seen in the insulating ferrimagnet yttrium iron garnet (YIG) [9], which has become the benchmark material for SSE studies [2]
In MgO/Fe3O4/Pt thin films, the magnon diffusion length (MDL) was extracted from SSE measurements using the linear response theory (LRT) [23] and found to be

Summary

Introduction

The spin Seebeck effect (SSE) was demonstrated in 2008 by Uchida et al and has since sparked a lot of interest for potential thermoelectric applications [1]. In the former case and for low conductivity magnets like Fe3O4, an important length scale for quantifying the maximum SSE efficiency is the magnon diffusion length (MDL) [19]. In MgO/Fe3O4/Pt thin films, the MDL was extracted from SSE measurements using the linear response theory (LRT) [23] and found to be

Results

Conclusion