The magnetism of BiFeO₃ powders

Conventional sintering and direct ball milling of Bi₂O₃ + Fe₂O₃ mixture were used for the fabrication of BiFeO₃ powders. The fabricated powders were performed annealing or high energy ball milling to vary the grain size from bottom-up or top-down. It was found that the magnetization of the powders synthesized by both methods plotted with the reciprocal of the grain size could be linearly fitted, indicating that the magnetism is from the finite size effect. Exchange bias phenomenon was observed after field cooling (FC) of the powders, confirming the magnetization is due to the uncompensated or canted surface spins. No spin glass behavior was found in these powders.