Comparative study of structural, magnetic and dielectric properties of CoFe2O4 @ BiFeO3 and BiFeO3 @ CoFe2O4 core-shell nanocomposites

Nano-sized CoFe2O4 (CFO), BiFeO3 (BFO) and their core-shell composites BFO@CFO and CFO@BFO were synthesized by chemical co-precipitation method. X-ray diffraction pattern confirmed the crystallinity and phase formation of bare CFO, BFO and their core-shell composites. Morphology and core-shell nature of these nanoparticles is justified by field emission scanning electron microscopy (FESEM) and high resolution transmission electron microscopy (HRTEM). Magnetization curve showed the weak ferromagnetic behaviour of BFO. Typical ferrimagnetic behaviour is shown by bare CFO and core-shell nanocomposites. The value of maximum magnetization, remanence magnetization and coercivity of CFO@ BFO were found to be greater than the BFO@ CFO. Also, CFO@ BFO showed the highest value of dielectric constant in the frequency range of 10(4)-10(6) Hz. Dielectric constant versus temperature curve of BFO and core-shell composites exhibit incongruity close to the antiferromagnetic transition temperature (370 degrees C) of BFO indicating presence of magnetoelectric (ME) coupling.