Effects of Grain Boundaries and Defects on Anisotropic Magnon Transport in Textured Sr14Cu24O41

TL;DR

This study investigates how grain boundaries and defects affect magnon transport in textured Sr14Cu24O41, revealing significant suppression of magnon thermal conductivity due to scattering at these structural imperfections.

Contribution

It provides the first detailed analysis of the impact of microstructural defects on anisotropic magnon transport in Sr14Cu24O41 using TEM and a kinetic scattering model.

Findings

Magnon mean free paths are reduced by grain boundaries and defects.

Magnon thermal conductivity is significantly suppressed compared to single crystals.

Low magnon transmission across grain boundaries is observed.

Abstract

The strong spin-spin exchange interaction in some low-dimensional magnetic materials can give rise to a high group velocity and thermal conductivity contribution from magnons. One example is the incommensurate layered compounds (Sr,Ca,La)14Cu24O41. The effects of grain boundaries and defects on quasi-one-dimensional magnon transport in these compounds are not well understood. Here we report the microstructures and anisotropic thermal transport properties of textured Sr14Cu24O41, which are prepared by solid-state reaction followed by spark plasma sintering. Transmission electron microscopy clearly reveals nano-layered grains and the presence of dislocations and planar defects. The thermal conductivity contribution and mean free paths of magnons in the textured samples are evaluated with the use of a kinetic model for one-dimensional magnon transport, and found to be suppressed significantly as compared to single crystals at low temperatures. The experimental results can be explained by a one-dimensional magnon-defect scattering model, provided that the magnon-grain boundary scattering mean free path in the anisotropic magnetic structure is smaller than the average length of these nano-layers along the c axis. The finding suggests low transmission coefficients for magnons across grain boundaries.