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

We investigate the temperature evolution of the electronic structure of ferromagnetic CaB(6) using ultrahigh resolution photoemission spectroscopy; the electronic structure of paramagnetic LaB(6) is used as a reference. High resolution spectra of CaB(6) reveal a 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 the B sublattice inducing partial localization in the mobile electrons and low electron density at epsilon(F) is important to achieve ferromagnetism in these systems.