On the Theory of Magnets with Competing Double Exchange and Superexchange Interactions

TL;DR

This paper develops a mean field theory to analyze the competition between ferromagnetic double exchange and antiferromagnetic superexchange in CMR materials, revealing that this competition results in incomplete magnetization saturation rather than spin canting.

Contribution

It introduces a single-site mean field model explicitly incorporating carrier-mediated ferromagnetism and superexchange, providing new insights into magnetic ordering in CMR materials.

Findings

Competition leads to ferro- or antiferromagnetic order with incomplete saturation

Contrasts previous results by showing no spin canting occurs

Discusses experimental implications of the magnetic states

Abstract

In the CMR materials, ferromagnetic double exchange (DE) presumably coexists with a direct nearest-neighbour antiferromagnetic interaction. We construct a single-site mean field theory that explicitly takes into account the different nature of carrier-mediated ferromagnetism vs. Heisenberg-like superexchange. We find, in contrast to previous results in the literature, that the competition between these two exchange interactions leads to ferro- or antiferromagnetic order with incomplete saturation of the magnetization (or sublattice magnetization), rather than spin canting. The associated experimental implications are discussed.