Enhanced ferromagnetism from electron-electron interactions in double exchange type models

TL;DR

This study demonstrates that including electron-electron interactions in double exchange models significantly enhances ferromagnetism and Curie temperature, especially when fermion numbers are low relative to local moments.

Contribution

It introduces a Monte Carlo approach that incorporates on-site electron-electron interactions into the double exchange model, revealing their impact on magnetic properties.

Findings

Moderate electron-electron interactions boost ferromagnetism.

Enhanced Curie temperature observed with interactions.

Significant effects when fermion count is low compared to local moments.

Abstract

The magnetic properties of a variety of materials with promise for technological applications have been described by models in which fermions are coupled to local moment spins. Monte Carlo studies of such models usually ignore electron-electron interactions, even though the energy scale corresponding to these interactions may be comparable to or larger than other relevant energy scales. In this work we add on-site interactions between fermions to the double exchange model which we study with a Monte Carlo scheme in which temporal fluctuations of local moment spins are fully accounted for and electron-electron interactions are treated at a mean field level. We show that when the number of fermions is considerably less than the number of local moments even moderate interactions can lead to significant enhancement of ferromagnetism and the Curie temperature.