Effects of oxygen content on the electric and magnetic properties of BiFeO3 compound

Multiferroic BiFeOδ (δ=2.67, 2.95 and 3.02) compound of various oxygen contents (δ) have been prepared by gel sol method. The influence of oxygen contents on the structure, electric and magnetic properties of BiFeO3 compound has been investigated. X-ray diffraction (XRD) measurements indicate that all the samples of BiFeOδ have the same crystal structure regardless of oxygen content. The SEM micrograph reveals microstructures comprising of grains with various sizes from 200 nm to 1 µm. XPS study confirms the coexistence of Fe3+ and Fe2+ ions in BiFeOδ compound. The M(H) curves exhibit weak ferromagnetic behavior with unsaturated magnetization at room temperature, independent of the oxygen content. The M(T) curves of suggest anti-ferromagnetic behavior with Neel temperature of ~370 °C for BiFeO2.95 and BiFeO3.02 samples and paramagnetic behavior of BiFeO2.67 sample from RT up to 500 °C. The experimental results show that the antiferromagnetic ordering is strongly correlated with the oxygen content and is almost entirely suppressed in BiFeOδ with δ=2.67. The effect of oxygen vacancies is to weaken the magnetic ordering rather than to enhance it as previously suggested in the literature.