Real-space visualization of short-range antiferromagnetic correlations in a magnetically enhanced thermoelectric

TL;DR

This study provides a real-space visualization of short-range antiferromagnetic correlations in MnTe, revealing their anisotropic nature and potential role in enhancing thermoelectric performance, supported by neutron scattering and ab initio calculations.

Contribution

The paper presents the first real-space imaging of magnetic correlations in a thermoelectric material, combining neutron scattering analysis with density functional theory.

Findings

Robust, nanometer-scale antiferromagnetic correlations persist above T_N.

Magnetic correlation length is longer along the c axis than in the ab plane.

Ab initio calculations accurately reproduce the observed anisotropic correlations.

Abstract

Short-range magnetic correlations can significantly increase the thermopower of magnetic semiconductors, representing a noteworthy development in the decades-long effort to develop high-performance thermoelectric materials. Here, we reveal the nature of the thermopower-enhancing magnetic correlations in the antiferromagnetic semiconductor MnTe. Using magnetic pair distribution function analysis of neutron scattering data, we obtain a detailed, real-space view of robust, nanometer-scale, antiferromagnetic correlations that persist into the paramagnetic phase above the N\'eel temperature $T_{\mathrm{N}}$ = 307 K. The magnetic correlation length in the paramagnetic state is significantly longer along the crystallographic $c$ axis than within the $ab$ plane, pointing to anisotropic magnetic interactions. Ab initio calculations of the spin-spin correlations using density functional theory in the disordered local moment approach reproduce this result with quantitative accuracy. These findings constitute the first real-space picture of short-range spin correlations in a magnetically enhanced thermoelectric and inform future efforts to optimize thermoelectric performance by magnetic means.