Microscopic probe of magnetic polarons in antiferromagnetic <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi mathvariant="normal">Eu</mml:mi><mml:mn>5</mml:mn></mml:msub><mml:msub><mml:mi mathvariant="normal">In</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mi mathvariant="normal">Sb</mml:mi><mml:mn>6</mml:mn></mml:msub></mml:math>
J. C. Souza, S. M. Thomas, E. D. Bauer, J. D. Thompson, F. Ronning, P. G. Pagliuso, P. F. S. Rosa
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 of the formation of magnetic polarons in antiferromagnetic ${\mathrm{Eu}}_{5}{\mathrm{In}}_{2}{\mathrm{Sb}}_{6}$. First, we observe a reduction of the ${\mathrm{Eu}}^{2+}$ ESR linewidth as a function of the applied magnetic field consistent with ferromagnetic clusters that are antiferromagnetically coupled. Additionally, the ${\mathrm{Eu}}^{2+}$ line shape changes markedly below ${T}^{\ensuremath{'}}\ensuremath{\sim}200$ K, a temperature scale that coincides with the onset of CMR. The combination of these two effects provides strong evidence that magnetic polarons grow in size below ${T}^{\ensuremath{'}}$ and start influencing the macroscopic properties of the system.