Mean field theory for double-perovskites

TL;DR

This paper develops a mean field theory for double perovskites, highlighting the role of electron correlations in accurately predicting the ferromagnetic critical temperature's dependence on electron doping.

Contribution

It introduces a Hubbard U term into the model, addressing the discrepancy between theory and experiment regarding critical temperature behavior.

Findings

Degenerate magnetic channels cause suppression of critical temperature.

Including Hubbard U breaks degeneracy, aligning theory with experimental trends.

Electron correlations are essential for accurate modeling of double perovskites.

Abstract

A mean field approximation of a model for double perovskites that takes into account the coupling between itinerant electron spins and localized spins is developed. As in previously reported theoretical results, and contrary to experimental observation, the critical temperature is suppressed for large electron density. An effective Heisenberg model reveals the cause of this discrepancy: the competition between degenerate antiferromagnetic and ferromagnetic channels. This degeneracy can be broken by the inclusion of a Hubbard-type U term. It is therefore suggested that electron correlation effects need to be incorporated in the minimal model of double perovskites in order to explain the experimental observation of increasing ferromagnetic critical temperature with increasing electron doping.