The magnetic augment in the nitrogen substituted bismuth ferrite

BiFeO₃ is a promising room temperature multiferroics which has drawn great attention in the last decades. The coupling of electric polarization and magnetism makes it a good candidate for device application. One remained problem is that the weak ferromagnetism of BiFeO₃ is suppressed by the incommensurate spin spiral structure. Efforts have been devoted by doping rear earth elements or transition metals at Bi site or Fe site to modify the spin spiral structure. In many cases the magnetization is improved at the price of losing the electric polarization due to the doping-in-duced ferroelectric-paraelectric phase transition. An alternative way of improving the magnetism which can also avoid the decline in ferroelectricity is doping in O site. We have successfully synthesized nitrogen substituted BiFeO₃ nanocrystals. The crystal of BiFeO_2.1N_0.9 remains a ferroelectricity-allowed R3c structure while the enhanced magnetic properties of BiFeO_2.1N_0.9 are observed at room temperature.