Structural transitions and multiferrocity in Ba and Co substituted nanosized bismuth ferrite

To investigate the effect of Ba2+ and Co2+ substitution on the multiferroic properties of the BiFeO3 (BFO) ceramic, Bi1-xBaxFe1-yCoyO3 (x = 0,y = 0 and x = 0.2, y = 0,0.015,0.03,0.04,0.05) ceramics were prepared using sol-gel method. Multiferroic properties of BFO have been improved considerably on Ba2+ and Co2+ substitution at Bi and Fe site, respectively. Full pattern fitting of the XRD profile pattern confirmed the structural transition from rhombohedral to pseudo-cubic phase. The magnetisation in BFO rises appreciably and found to be 0.463 emu/g for Bi1-xBaxFe1-yCoyO3 (x = 0.2, y = 0.05) ceramic nanoparticles. The abrupt increase in magnetization for Bi0.8Ba0.2Fe0.95Co0.05O3 is due to anti-ferromagnetic orbital ordering among Fe/Co ions. The orbital ordering among the ions would change the low spin state of the Co2+ ions to high spin state and results in increased magnetization. Beside, the Co substitution is found helpful in reducing the coercivity of the magnetic nanoparticles for their application as magnetic sensors. The Ferroelectric behavior of Ba and Co substituted samples revealed that increase in maximum polarization with increasing Co content is due to interactions among different Jahn-Teller active Co2+ ions. Moreover, the slimmer polarization-electric field (P-E) loops on increasing Co content implying the relaxor ferroelectric behavior of the samples.