Microscopic probe of magnetic polarons in antiferromagnetic Eu$_{5}$In$_{2}$Sb$_{6}$

TL;DR

This study uses electron spin resonance to provide microscopic evidence of magnetic polaron formation in antiferromagnetic Eu$_{5}$In$_{2}$Sb$_{6}$, linking polaron growth to colossal magnetoresistance phenomena.

Contribution

It demonstrates the presence of magnetic polarons in an antiferromagnetic material using ESR, a novel insight into CMR mechanisms in such systems.

Findings

ESR linewidth reduction indicates ferromagnetic clusters within antiferromagnetic matrix

Line shape changes below T' ~ 200 K coincide with CMR onset

Magnetic polarons grow below T', affecting macroscopic properties

Abstract

Colossal magnetoresistance (CMR) emerges from intertwined spin and charge degrees of freedom in the form of ferromagnetic clusters also known as trapped magnetic polarons. As a result, CMR is rarely observed in antiferromagnetic materials. Here we use electron spin resonance (ESR) to reveal microscopic evidence for the formation of magnetic polarons in antiferromagnetic Eu$_{5}$In$_{2}$Sb$_{6}$. First, we observe a reduction of the Eu$^{2+}$ ESR linewidth as a function of the applied magnetic field consistent with ferromagnetic clusters that are antiferromagnetically coupled. Additionally, the Eu$^{2+}$ lineshape changes markedly below T' ~ 200 K, a temperature scale that coincides with the onset of CMR. The combination of these two effects provide strong evidence that magnetic polarons grow in size below T' and start influencing the macroscopic properties of the system.