Antiferromagnetic Order and Phase Coexistence in Antisite Disordered Double Perovskites

TL;DR

This study investigates how antisite disorder affects antiferromagnetic order in double perovskites, revealing that AF phases are more robust and conductive than ferromagnetic phases under disorder, with coexistence regions identified.

Contribution

It demonstrates that antiferromagnetic order persists and can even be more conductive than ferromagnetism in disordered double perovskites, highlighting phase coexistence and disorder effects.

Findings

AF order is less suppressed by disorder than ferromagnetism.

AF phases are metallic and more conductive than ferromagnetic phases.

Identifies a phase coexistence window between ferromagnetic and AF phases.

Abstract

In addition to the well known ferromagnetism, double perovskites are also expected to exhibit antiferromagnetic (AF) order driven by electron delocalisation. This has been seen in model Hamiltonian studies and confirmed via ab initio calculations. The AF phases should occur, for example, on sufficient electron doping of materials like Sr_2FeMoO_6 (SFMO) via La substitution for Sr. Clear experimental indication of such AF order is limited, possibly because of increase in antisite disorder with La doping on SFMO, although intriguing signatures of non ferromagnetic behaviour are seen. We study the survival of electronically driven antiferromagnetism in the presence of spatially correlated antisite disorder and extract the signals in magnetism and transport. We discover that A and G type AF order, that is predicted in the clean limit, is actually suppressed less strongly than ferromagnetism by antisite disorder. The AF phases are metallic, and, remarkably, more conducting that the ferromagnet for similar antisite disorder. We also highlight the phase coexistence window that connects the ferromagnetic regime to the A type antiferromagnetic phase.