# Contrasting the magnetism in La$_{2-x}$Sr$_x$FeCoO$_6$ ($x$ = 0, 1, 2) double perovskites: the role of electronic and cationic disorder

## TL;DR

This study compares the magnetic properties of La$_{2-x}$Sr$_x$FeCoO$_6$ double perovskites, revealing how electronic and cationic disorder influence the transition from long-range antiferromagnetism to short-range glassy magnetism.

## Contribution

It provides a comprehensive experimental and computational analysis of how disorder and electronic structure affect magnetism in La$_{2-x}$Sr$_x$FeCoO$_6$ compounds, highlighting the role of electronic degrees of freedom.

## Key findings

- La$_2$FeCoO$_6$ is a long-range ordered antiferromagnet with a transition at 270 K.
- Replacing La with Sr induces a transition to short-range glassy magnetism.
- Density functional theory shows La$_2$FeCoO$_6$ is insulating, while Sr-doped variants are metallic.

## Abstract

The magnetism of the double perovskite compounds \SLFCOx\ ($x$ = 0, 1, 2) are contrasted using magnetization, neutron diffraction and electron paramagnetic resonance with the support from density functional theory calculations. \LFCO\ is identified as a long-range ordered antiferromagnet displaying a near-room temperature transition at $T_N$ = 270~K, accompanied by a low temperature structural phase transition at $T_S$ = 200~K. The structural phase transformation at $T_S$ occurs from $R\overline{3}c$ at 300~K to $Pnma$ at 200~K. The density functional theory calculations support an insulating non-compensated AFM structure. The long-range ordered magnetism of \LFCO\ transforms to short-range glassy magnetism as La is replaced with Sr in the other two compounds. The magnetism of \LFCO\ is differentiated from the non-equilibrium glassy features of \SFCO\ and \SLFCO\ using the {\em cooling-and-heating-in-unequal-fields} (CHUF) magnetization protocols. This contransting magnetism in the \SLFCOx\ series is evidenced in electron paramegnetic resonance studies. The electronic density-of-states estimated using the density functional theory calculations contrast the insulating feature of \LFCO\ from the metallic nature of \SFCO. From the present suite of experimental and computational results on \SLFCOx, it emerges that the electronic degrees of freedom, along with antisite disorder, play an important role in controlling the magnetism observed in double perovskites.