A Magnetic Model for the Ordered Double Perovskites

TL;DR

This paper develops an effective magnetic spin model for double perovskites, capturing their magnetic interactions and properties, and compares it with full numerical solutions, providing a practical approach for studying these materials.

Contribution

It introduces a simplified magnetic model derived from the spin-fermion problem for double perovskites, applicable even with antisite disorder, and validates it against detailed numerical solutions.

Findings

The effective exchange can be estimated from electronic parameters.

Monte Carlo simulations agree reasonably with full numerical solutions.

The model can be generalized to include antisite disorder.

Abstract

We construct an effective spin model from the coupled spin-fermion problem appropriate to double perovskites of the form A_2BB'O_6. The magnetic model that emerges is reminiscent of double exchange and we illustrate this `reduction' in detail for the case of perfect B-B' structural order, i.e, no antisite disorder. We estimate the effective exchange between the magnetic B ions in terms of the electronic parameters, study the `classical' magnetic model using Monte Carlo techniques, and compare this approach to a full numerical solution of the spin-fermion problem. The agreement is reasonable, and promises a quick estimate of magnetic properties when coupled with ab initio electronic structure. The scheme generalises to the presence of antisite disorder.