Structural modification and enhanced magnetic properties with two phonon modes in Ca–Co codoped BiFeO3 nanoparticles

Bi1−xCaxFe1−xCoxO3 nanoparticles with x=0.0, 0.05, 0.10 and 0.15 were successfully synthesized by cost effective tartaric acid based sol–gel route. The alkali earth metal Ca2+ ions and transition metal Co3+ ions codoping at A and B-sites of BiFeO3 results in structural distortion and phase transformation. Rietveld refinement of XRD patterns suggested the coexistence of rhombohedral and orthorhombic phases in codoped BiFeO3 samples. Both XRD and Raman scattering studies showed the compressive lattice distortion in the samples induced by codoping of Ca2+ and Co3+ ions. Two-phonon Raman spectra exhibited the improvement of magnetization in these samples. X-ray photoelectron spectroscopy (XPS) showed the dominancy of Fe3+ and Co3+ oxidation states along with the shifting of the binding energy of Bi 4f orbital which confirms the substitution Ca2+ at Bi-site. The magnetic study showed the enhancement in room temperature ferromagnetic behavior with co-substitution consistent with Rama analysis. The gradual change in line shape of electron spin resonance spectra indicated the local distortion induced by codoping.