Surface agglomeration is beneficial for release of magnetic property via research of rare earth (RE) element-substitution

BiFeO₃ (BFO) thin films and Rare-Earth (RE) element substitutions were successfully fabricated on silicon substrates by sol-gel technology. Multiferroic properties of BFO had been improved considerably on RE (La, Ho, Er)-substitution at Bi site. The RE-substitution principle was presented in Fig. 1(the simulative images of ions matching). The single phase and the perovskite based rhombohedral structure with R3c space group of BFO and RE-substitution films were confirmed through the full pattern fitting of surface and section XRD profiles. There were obvious agglomeration phenomena for RE-substitution films via FESEM patterns, and the AFM images shown that the RE-substation films possessed smoother surface texture comparing with the BFO. The RE-substitution films showed higher saturation magnetization (Ms) and remanent magnetization (Mr) due to the reduced concentration of defects (oxygen vacancy), RE ions with smaller radii size (size effect) and surface structure of compactness. Fe³⁺ and O^2- ions play an essential role in superexchange interaction, the XPS, surface and vertical EDS images revealed increasing tendency of Fe³⁺ ions and O^2- ions.