Thermodynamic evidence for polaron stabilization inside the antiferromagnetic order of Eu$_5$In$_2$Sb$_6$

TL;DR

This study provides thermodynamic evidence for magnetic polaron formation in Eu$_5$In$_2$Sb$_6$, revealing their anisotropic nature and stabilization within antiferromagnetic order, offering insights into colossal magnetoresistance mechanisms beyond manganites.

Contribution

It demonstrates the existence and anisotropic behavior of magnetic polarons in Eu$_5$In$_2$Sb$_6$ and their stabilization within antiferromagnetic order, a novel insight into correlated magnetic materials.

Findings

Magnetic polarons form well above the magnetic ordering temperature.

Polarons exhibit anisotropic extent along different crystallographic directions.

Ferromagnetic polarons are stabilized within the antiferromagnetic phase at lower temperatures.

Abstract

Materials exhibiting electronic inhomogeneities at the nanometer scale have enormous potential for applications. Magnetic polarons are one such type of inhomogeneity which link the electronic, magnetic and lattice degrees of freedom in correlated matter and often give rise to colossal magnetoresistance. Here, we investigate single crystals of Eu$_5$In$_2$Sb$_6$ by thermal expansion and magnetostriction along different crystallographic directions. These data provide compelling evidence for the formation of magnetic polarons in Eu$_5$In$_2$Sb$_6$ well above the magnetic ordering temperature. More specifically, our results are consistent with anisotropic polarons with varying extent along the different crystallographic directions. A crossover revealed within the magnetically ordered phase can be associated with a surprising stabilization of ferromagnetic polarons within the global antiferromagnetic order upon decreasing temperature. These findings make Eu$_5$In$_2$Sb$_6$ a rare example of such coexisting and competing magnetic orders and, importantly, shed new light on colossal magnetoresistive behavior beyond manganites.