CaB6 : a new semiconducting material for spin electronics

Ferromagnetism was recently observed at unexpectedly high temperatures in La-doped CaB6. The starting point of all theoretical proposals to explain this observation is a semimetallic electronic structure calculated for CaB6 within the local density approximation. Here we report the results of parameter-free quasiparticle calculations of the single-particle excitation spectrum which show that CaB6 is not a semimetal but a semiconductor with a band gap of 0.8¿0.1 eV. Magnetism in LaxCa1-xB6 occurs just on the metallic side of a Mott transition in the La-induced impurity band.