Effect of layer number on ferromagnetic properties in aurivillius Bi4Bin-3Fen-3.2Co0.2Ti3O3n+3 ceramics

• The physical properties of the layer-structured BFTO could be greatly affected by the layer number n.
• Partial substituted of Co for Fe could break the AFM or PFM state in pure BFTO at room temperature, thus exhibits ferromagnetization.
• A systematic investigation of the influence of layer number n on the room temperature ferromagnetic properties of the Co-substituted BFTO has been done.

Aurivillius Bi4Bin-3Fen-3.2Co0.2Ti3O3n+3 (BFCT, n=4–7) ceramics were prepared by the hot-press method. X-ray diffraction and high-resolution transmission electron microscopy analysis indicate a successful synthesis of pure phase BFCT samples. All samples show significant magnetic moments at the room temperature. Interestingly, the remanent magnetization (2Mr) increases with the increase of n, which was found to be 21.53 emu/mol, 413.49 emu/mol, 472.78 emu/mol and 727.03 emu/mol for n=4, 5, 6 and 7 ceramics, respectively. This phenomenon can be ascribed to the increased coupling probability of Fe-O-Co with increasing n. Besides, the odd-layered compounds are likely to be beneficial for enhancing the 2Mr, due to that their crystalline structures may endure larger distortions when compared with the even-layered compounds.