Antiferromagnetic metal phases in double perovskites having strong antisite defect concentrations

TL;DR

This paper explores how strong antisite defects in double perovskites like Sr₂FeMoO₆ can still lead to an antiferromagnetic metal phase through a novel hopping mechanism, supported by variational calculations.

Contribution

It proposes a new mechanism for stabilizing antiferromagnetic metal phases in defect-rich double perovskites, extending previous theories to more realistic defect scenarios.

Findings

Strong antisite defects can induce AFM metallic phases.

Phase segregation favors A-type AFM over G-type AFM.

Kinetic energy considerations drive phase stabilization.

Abstract

Recently an antiferromagnetic metal phase has been proposed in double perovskites materials like Sr$_{2}$FeMoO$_{6}$ (SFMO), when electron doped. This material has been found to change from half-metallic ferromagnet to antiferromagnetic metal (AFM) upon La-overdoping. The original proposition of such an AFM phase was made for clean samples, but the experimental realization of La-overdoped SFMO has been found to contain a substantial fraction of antisite defects. A phase segregation into alternate Fe and Mo rich regions was observed. In this paper we propose a possible scenario in which this type of strong antisite concentration can still result in an antiferromagnetic metal phase, by a novel hopping driven mechanism. Using variational calculations, we find that proliferation of such phase segregated domain regions can also result in the stabilization of an A-type AFM over the G-type AFM based on kinetic energy considerations.