Colossal Magnetoresistance and Phonon Driven Exchange Dynamics in Eu$_5$Sn$_2$As$_6$

TL;DR

This study investigates Eu$_5$Sn$_2$As$_6$, revealing how magnetic field influences thermal conductivity and magnetostriction, linking phonon behavior to colossal magnetoresistance through exchange dynamics.

Contribution

It demonstrates the role of phonon-driven exchange dynamics and magnetostriction in Eu$_5$Sn$_2$As$_6$, providing new insights into its colossal magnetoresistance mechanism.

Findings

Thermal conductivity and magnetostriction are strongly field-dependent.

Field-enhancement of thermal conductivity is due to lifting of spin degeneracy.

Exchange frustration suppression of phonon scattering drives electron delocalization.

Abstract

The emergence of colossal magnetoresistance in a new generation of Eu$^{2+}$-based antiferromagnets is intriguing given stark contrasts to the archetypal perovskite manganites and doped Eu-chalcogenides. In this study the thermal conductivity and magnetostriction of Eu$_5$Sn$_2$As$_6$ -- one such representative -- have been measured to better understand the role of the crystal lattice. Both properties are strongly field-dependent and mirror the magnetization, saturating once the Eu$^{2+}$ moments are polarized. The field-enhancement of the phonon-dominated thermal conductivity is interpreted through the lifting of a degeneracy of spin configurations, and the subsequent saturation due to quenched magnetostrain in high field. Comparison with spin-glass insulators suggests that this phenomenon is not a byproduct but rather the driver of electron delocalization due to the suppression of strong phonon scattering arising from exchange frustration.