Room-temperature ferromagnetic/ferroelectric BiFeO3 synthesized by a self-catalyzed fast reaction process

Bismuth ferrite BiFeO3 has attracted a great deal of interest because of its multiferroic properties. However, BiFeO3 synthesized by conventional methods in the forms of single crystals, ceramics or thin films only exhibit ferroelectricity and antiferromagnetic order at room temperature, with weak ferromagnetism appearing at very low temperatures. To fully explore the potential of multiferroism in such applications as new memory devices, it is necessary to synthesize materials that show ferromagnetic order at room temperature as well, which will a priori allow for magnetoelectric coupling. In this paper, we report a new synthetic technique for the synthesis of BiFeO3 that exhibits unusual ferromagnetic properties. This method involves a low temperature fast solid state reaction based on tartaric acid. The mechanism of the reaction deduced from thermogravimetric analysis (TGA) and differential thermal analysis (TGA) suggests that a self-catalyzed process in the presence of iron and bismuth oxides triggers the oxidation of tartaric acid at low temperature and gives out a large amount of heat, which, in turn, leads to the formation of BiFeO3. The BiFeO3 synthesized in this way is ferromagnetic. The origin of the unusual ferromagnetism is supposed to be associated with point defects of oxygen vacancies generated during the self-catalyzed extremely fast exothermic reaction, which suppress the spin circular cycloid in BiFeO3. Ferroelectric hysteresis loops are displayed in the BiFeO3 samples. The presence of room temperature ferromagnetic and ferroelectric orders makes BiFeO3 a truly multiferroic material potentially interesting in such applications as magnetoelectric devices.