Hund's rule and metallic ferromagnetism

TL;DR

This paper proves that in certain two-band models with strong Hund's rule interactions, the ground states exhibit metallic ferromagnetism characterized by macroscopic magnetization and delocalized electrons.

Contribution

It provides a rigorous proof that large on-site exchange anisotropy induces metallic ferromagnetism in specific tight-binding models.

Findings

Ground states show macroscopic magnetization

Electrons are spatially delocalized

No energy gap for kinetic excitations

Abstract

We study tight-binding models of itinerant electrons in two different bands, with effective on-site interactions expressing Coulomb repulsion and Hund's rule. We prove that, for sufficiently large on-site exchange anisotropy, all ground states show metallic ferromagnetism: They exhibit a macroscopic magnetization, a macroscopic fraction of the electrons is spatially delocalized, and there is no energy gap for kinetic excitations.