Enhanced ferromagnetism in BiFeO3 powders by rapid combustion of graphite powders

The magnetoelectric applications of BiFeO3 are strongly limited by the very weak ferromagnetism, due to the cycloidal modulated antiferromagnetic structure. In this paper, a rapid combustion method was adopted to prepare BiFeO3 powders. The amorphous BiFeO3 precursors prepared by sol-gel method were mixed with graphite powders and calcined at 350 °C for 5 minutes. BiFeO3 powders were crystallized well with grain size of 30 nm due to the local high temperature during the rapid combustion of graphite powders in short time, and the high crystallinity was confirmed by the Raman spectra. Clear room temperature ferromagnetism has been observed, with significantly large coercivity of 0.19 kOe and magnetization of 0.48 emu/g at 10 kOe, which is much larger than that of BiFeO3 powders sintered at 600 °C (negligible small coercivity and 0.092 emu/g at 10 kOe). The enhancement of ferromagnetism has been attributed to the suppression of the cancellation of canted spins due to the much smaller crystallite size than the cycloidal modulation period.