Origin of the magnetism in CaB6: A first-principles study

Through systematic density functional calculations, we revealed that the weak ferromagnetism in CaB6 and related materials stems from the joint effect of boron vacancies and impurities. Each boron vacancy introduces strongly localized gap states around its first-neighbor B atom right above the Fermi level. The partial occupation of these gap states caused by either lattice distortion or addition charge triggers magnetic instability and the local magnetic moment can be as large as 0.8-1.2 mu(B) in various cases.