Effect of Solvents on the Ferromagnetic Behavior of Undoped BiFeO3 Prepared by Sol-Gel

We here report the preparation of undoped BiFeO₃ (BFO) thin films with sol-gel method using two solvents, i.e., acetic acid (AA) and ethylene glycol (EG). Films are annealed in the temperature range 100-300 °C for 60 mins. Films deposited using AA show the presence of bismuth rich phase Bi₄₆Fe₂O₇₂ along with BFO in the intermediary conditions. Pure phase BFO is obtained when films are deposited using EG as a solvent even under as-deposited conditions, and the pure phase persists after annealing in the temperature range 100 °C-300 °C. This is the lowest temperature reported for the preparation of phase pure BFO. Bandgap of AA-based films lies in the range 2.58-2.64 eV and that of EG-based films in the range 2.77-2.81 eV. Reduced value of dielectric constant, in AA-based films, is because of the presence of bismuth rich impurity phase as compared with the films prepared using EG. Bands in FTIR spectra at 487 and 552 cm^-1 are characteristic bands of FeO₆ and BiO₆ groups, indicating the formation of BFO. Films deposited using AA show weak ferromagnetic behavior, while those deposited using EG show strong ferromagnetic behavior as opposed to antiferromagnetic nature of BFO, due to suppression of spiral spin structure.