Enhancing the magnetic characteristics of BiFeO3 nanoparticles by Ca, Ba co-doping

Multiferroic nanoparticles (NPs) of pristine and Ca, Ba co-doped BiFeO3 were synthesized by a facile sol–gel route. Co-doping was done by fixing the total dopant concentration at 5 mol% and then the relative concentrations of Ca and Ba was varied. Structural, optical and magnetic properties of the NPs were investigated using different techniques. UV–Vis absorption spectra of BiFeO3 NPs showed a substantial blue shift of ∼100 nm (530 nm → 430 nm) on Ca, Ba co-doping which corresponds to increase in band gap by 0.5 eV. 57Fe Mössbauer spectroscopy confirmed that iron is present only in 3+ valence state in all co-doped samples. The coercive field increased by 18 times for Bi0.95Ca0.01Ba0.04FeO3 samples, which is the maximum enhancement, observed amongst all the 5 mol% doped samples. At the equimolar (2.5 mol% each) concentration of co-dopants, the coercive field shows a significant enhancement of about 9 times (220 Oe → 2014 Oe) with concomitant increase in saturation magnetization by 7 times. Thus, equimolar co-doping causes simultaneous enhancement of the twin aspects of magnetic properties thereby making them better suited for device applications.