Origin of ferromagnetism in polycrystalline Ca1+δB6 (-0.05<δ<0.05) ceramics

We have investigated systematically the relationship of ferromagnetic properties of polycrystalline Ca1+δB6 ceramics with Ca content, as δ ranges from −0.05 to 0.05. We demonstrated that the origin of the high-temperature ferromagnetism observed in CaB6 can be ascribed to the existence of Fe containing impurity phases. For δ<0 (Ca deficiency) Fe exists as boride, whereas for δ>0 (excess Ca) it is present as oxide. The dependence of magnetization with the nominal stoichiometry of Ca1+δB6 can be understood from the evolution of Fe boride and oxide phase in the materials.