BiFeO3 is the only single-phase material that simultaneously exhibits ferroelectric and antiferro/ferromagnetic properties at room temperature. This peculiar behaviour of this material makes it a potential candidate for several applications such as in spintronics, memory storage devices, sensors, and actuators. However, weak canted magnetic moments superimposed by a spin spiral structure with a 62-64 nm wavelength cancel any net magnetization and limit the practical device applications. Net magnetization can be enhanced by suitable doping, inducing strain, and reducing crystallite size.
Synthesis of pure BiFeO3 is still challenging. Traditionally, the synthesis of bulk BiFeO3 through a solid-state reaction route involves a chemical reaction between Bi2O3 and Fe2O3. Reaction occurs through ionic diffusion, often resulting in a larger fraction of secondary phases such as Bi2Fe4O¬9. Faster reaction rates usually translate into purer phases. Various techniques have been adopted to prepare BiFeO3, including microwave sintering, spark plasma sintering, and rapid liquid phase sintering. Magnetic properties are often enhanced when the crystallite size is less than 62-64 nm. Further, obtaining nanocrystalline BiFeO3 through conventional sintering is difficult.
The aim of the present research is to prepare phase pure nanocrystalline BiFeO3 using novel approaches with Bi and Fe metallic powders. These metallic powders are ball milled for 10 -20 h followed by annealing at 700 - 850 °C for 1 - 60 min. Relatively pure samples were obtained with flower-like morphology for 10 h ball-milled powder annealed at 800 °C for 2 min. Preliminary results have shown that size, strain, and morphology can be carefully controlled to obtain colossal enhancement in the magnetic properties. Synthesis of BiFeO3 and Cr-doped BiFeO3 has been also carried out using ball-milled mixtures of oxide powders (10 h) followed by spark plasma sintering at 650 °C and 5 min hold time with applied pressure of 50 MPa. It is observed that Cr doping enhances the electrical properties. Encouraged by the preliminary results, the current work proposes further exploring the magnetic, electric, and magnetoelectric coupling properties vis-a-vis synthesis route combined with the doping effects.

Keywords: BiFeO3; Ball milling; Magnetic Properties; Doping; Spark plasma sintering; Multiferroics