Fine Control of Multiferroic Features of Nanoscale BiFeO₃ Powders Synthesized by Microwave-Assisted Solid-State Reaction

Variations in the multiferroic properties of BiFeO₃ (BFO) powders were investigated with respect to the crystallite size and Gd-doping. Nanoscale BFO powders with an average particle size range of ~ 30–80 nm were synthesized by a solid-state reaction using microwave-assisted heat treatment with Bi(NO₃)₃·5H₂0, FeC₂O₄·2H₂O and Gd(NO₃)₃·6H₂O as source precursors supplying Bi, Fe, and Gd, respectively. These were heat-treated at temperatures ranging from 200 to 700 °C. The reaction led to the formation of crystallite powders with a particle size of a few tens of nanometers. It was confirmed that these samples had multiferroic properties at room temperature, and the value of M_s varied significantly from ferromagnetic to antiferromagnetic and vice versa with the size of the powders. In particular, ferromagnetic and ferroelectric features were observed when the size of the BFO powder was < ~ 30 nm (half of the spin-canted cycle). As the crystallite size was reduced to that corresponding to half of the spin canted cycle, the value of Ms increased by 8.8 times from 1.41 to 12.46 memu/g. Compared to pure BFO, when Gd was doped, Ms values increased by ~ 60% and 240% in ~ 30 nm and ~ 60 nm particle-sized powders. Graphical Abstract: [Figure not available: see fulltext.].