A Theory of Magnets with Competing Double Exchange and Superexchange Interactions

TL;DR

This paper develops a mean field theory to analyze the competition between double exchange and superexchange interactions in CMR materials, revealing new magnetic ordering behaviors and contrasting previous canted spin results.

Contribution

It introduces a single site mean field approach emphasizing hopping-mediated double exchange, providing new insights into magnetic orderings in CMR materials.

Findings

Competition leads to ferro- or antiferromagnetic order

Incomplete saturation of lattice magnetization observed

Contrasts with previous canted spin arrangements

Abstract

We study the competition between ferromagnetic double exchange (DE) and nearest-neighbour antiferromagnetic exchange in CMR materials. Towards this end, a single site mean field theory is proposed which emphasizes the hopping-mediated nature of the DE contribution. We find that the competition between these two exchange interactions leads to ferro- or antiferromagnetic order with incomplete saturation of the (sub)lattice magnetization. This conclusion is in contrast to previous results in the literature which find a canted spin arrangement under similar circumstances. We attribute this difference to the highly anisotropic exchange interactions used elsewhere. The associated experimental implications are discussed.