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

Abstract

We investigate the temperature evolution of the electronic structure of ferromagnetic CaB₆ using ultrahigh resolution photoemission spectroscopy; the electronic structure of paramagnetic LaB₆ is used as a reference. High resolution spectra of CaB₆ reveal a finite density of states at the Fermi level ε_F at all the temperatures and evidence of impurity induced localized features in the vicinity of ε_F, which are absent in the spectra of LaB₆. Analysis of the high resolution spectra suggests that disorder in the B sublattice inducing partial localization in the mobile electrons and low electron density at ε_F is important to achieve ferromagnetism in these systems.