Excitonic ferromagnetism in the hexaborides

TL;DR

This paper proposes that excitonic insulator condensation in doped hexaborides explains their unexpected ferromagnetism, highlighting a novel mechanism for magnetic ordering in these materials.

Contribution

It introduces a new theoretical framework linking excitonic insulator states to ferromagnetism in doped hexaborides, which was not previously understood.

Findings

Doped hexaborides exhibit ferromagnetism due to excitonic condensates.

The mechanism explains high Curie temperatures with small magnetic moments.

The theory aligns with experimental observations in Ca_{1-x}La_xB_6.

Abstract

A ferromagnet with a small spontaneous moment but with a high Curie temperature can be obtained by doping an excitonic insulator made from a spin triplet exciton condensate. Such a condensate can occur in a semimetal with a small overlap or a semiconductor with a small bandgap. We propose that it is responsible for the unexpected ferromagnetism in the doped hexaboride material Ca_{1-x}La_xB_6.