Revelation of the role of impurities and conduction electron density in the high resolution photoemission study of ferromagnetic hexaborides

TL;DR

This study uses ultra-high resolution photoemission spectroscopy to explore how impurities and conduction electron density influence ferromagnetism in hexaborides, revealing persistent states at the Fermi level and impurity-induced features.

Contribution

It demonstrates the role of impurity-induced localization and low electron density at the Fermi level in stabilizing ferromagnetism in CaB₆.

Findings

Finite density of states at the Fermi level in CaB₆ at all temperatures.

Presence of impurity-induced localized features near the Fermi level.

Disorder in B-sublattice linked to ferromagnetism.

Abstract

We investigate the temperature evolution of the electronic structure of ferromagnetic CaB$_6$ using ultra-high resolution photoemission spectroscopy; electronic structure of paramagnetic LaB$_6$ is used as a reference. High resolution spectra of CaB$_6$ reveal finite density of states at the Fermi level, $\epsilon_F$ at all the temperatures and evidence of impurity induced localized features in the vicinity of $\epsilon_F$, which are absent in the spectra of LaB$_6$. Analysis of the high resolution spectra suggests that disorder in B-sublattice inducing partial localization in the mobile electrons and low electron density at $\epsilon_F$ is important to achieve ferromagnetism in these systems.