Large Magnetoresistance and Jahn Teller effect in Sr$_2$FeCoO$_6$

TL;DR

This study reveals large magnetoresistance and Jahn-Teller distortion in Sr$_2$FeCoO$_6$, linking structural disorder, mixed valence states, and spin glass behavior to its magnetic and electronic properties.

Contribution

It provides new insights into the interplay of site disorder, valence states, and Jahn-Teller effects in Sr$_2$FeCoO$_6$, demonstrating its significant magnetoresistance and complex magnetic interactions.

Findings

Large negative magnetoresistance (~63%) at 14K in 12T field.

Evidence of Jahn-Teller distortion at Co$^{3+}$-O$_6$ complex.

Presence of spin glass state due to competing magnetic interactions.

Abstract

Neutron diffraction measurement on the spin glass double perovskite Sr$_2$FeCoO$_6$ reveals site disorder as well as Co$^{3+}$ intermediate spin state. In addition, multiple valence states of Fe and Co are confirmed through M\"{o}ssbauer and X-ray photoelectron spectroscopy. The structural disorder and multiple valence lead to competing ferromagnetic and antiferromagnetic interactions and subsequently to a spin glass state, which is reflected in the form of an additional $T$-linear contribution at low temperatures in specific heat. A clear evidence of Jahn-Teller distortion at the Co$^{3+}$-O$_6$ complex is observed and incorporating the physics of Jahn-Teller effect, the presence of localized magnetic moment is shown. A large, negative and anomalous magnetoresistance of $\approx$ 63% at 14K in 12T applied field is observed for Sr$_2$FeCoO$_6$. The observed magnetoresistance could be explained by applying a semi-empirical fit consisting of a negative and a positive contribution and show that the negative magnetoresistance is due to spin scattering of carriers by localized magnetic moments in the spin glass phase.