Effect of nonmagnetic alkaline-earth dopants on magnetic properties of BiFeO3 thin films

Bi0.95A0.05FeO3 (A = Ba, Sr, Ca) thin films were deposited on (111) Pt/Ti/SiO2/Si substrates via chemical solution deposition. The magnetization of the doped specimens increases sharply as compared to that of pure BiFeO3, and it increases as the doped ionic radius gets larger. X-ray diffraction analysis reveals that the films are single phase, and no other extra magnetic phases are detected. X-ray photoelectron spectroscopy analysis suggests that the content of Fe3+ increases and that that of Fe2+ decreases. According to the x-ray diffraction and Raman analyses, there are corresponding changes in the lattice parameters and the Raman spectra as the doped ionic radius gets larger. These results indicate that neither the magnetic coupling of Fe2+ nor the parasitic magnetic phases could be the origin of the magnetization improvement, and we consider that the magnetization improvement mainly originates from the doped ionic radius size effect.