Ferromagnetism in CaB6 Original Research Article

The possibility of metallic ferromagnetism in the ground states of semi-metallic system is theoretically studied in connection with the recent experimental findings of weak-ferromagnetism in divalent CaB6. Within the scheme of the mean-field approximation on the extended Hubbard model, we found that the presence of a single pair of semi-metallic bands is required for the appearance of such ferromagnetic metal (FM) under the Coulomb and exchange interactions. Our calculation based on the realistic models of CaB6 in three-dimension shows that such a FM is destabilized if the three different pairs of semi-metallic bands are included. This suggests that the ferromagnetism is not realized in the cubic CaB6 unless there is some possible local removal of the cubic symmetry which makes the system tetragonal.