Reconstruction of an effective magnon mean free path distribution from spin Seebeck measurements in thin films

TL;DR

This study reconstructs the magnon mean free path distribution in thin films using spin Seebeck measurements, revealing diverse contributions of magnons with different MFPs to the thermoelectric effect.

Contribution

It adapts a phonon MFP reconstruction algorithm to magnons, providing the first detailed distribution of magnon MFPs from experimental data.

Findings

Magnons have a broad MFP distribution affecting the LSSE.

Different magnon MFPs contribute variably to the LSSE.

Magnon MFPs extend beyond typical average values.

Abstract

A thorough understanding of the mean-free-path (MFP) distribution of the energy carriers is crucial to engineer and tune the transport properties of materials. In this context, a significant body of work has investigated the phonon and electron MFP distribution, however, similar studies of the magnon MFP distribution have not been carried out so far. In this work, we used thickness-dependence measurements of the longitudinal spin Seebeck (LSSE) effect of yttrium iron garnet films to reconstruct the cumulative distribution of a SSE related effective magnon MFP. By using the experimental data reported by Guo et al. [Phys. Rev. X 6, 031012 (2016)], we adapted the phonon MFP reconstruction algorithm proposed by A.J. Minnich, [Phys. Rev. Lett. 109, 205901 (2012)] and apply it to magnons. The reconstruction showed that magnons with different MFP contribute in different manner to the total LSSE and the effective magnon MFP distribution spreads far beyond their typical averaged values.