Enhanced Magnetic Properties of Co-Doped BiFeO₃ Thin Films via Structural Progression

Co³⁺ doping in BiFeO₃ is expected to be an effective method for improving its magnetic properties. In this work, pristine BiFeO₃ (BFO) and doped BiFe_1-xCo_xO₃ (BFC_xO, x = 0.01, 0.03, 0.05, 0.07 and 0.10) composite thin films were successfully synthesized by a sol-gel technique. XRD and Raman spectra indicate that the Co³⁺ ions are substituted for the Fe³⁺ ion sites in the BFO rhombohedral lattice. Raman vibration of oxygen octahedron is obviously weakened due to the lattice distortion induced by the size mismatch between two B-site cations (Fe³⁺ and Co³⁺ ions), which has an impact on the magnetic properties of BFC_xO. SEM images reveal a denser agglomeration in Co-doped samples. TEM results indicate that the average size of grains is reduced due to the Co³⁺ substitution. XPS measurements illustrate that the replacement of Fe³⁺ with Co³⁺ effectively suppresses the generation of oxygen defects and increases the concentration of Fe³⁺ ions at the B-site of perovskite lattice. Vibrating sample magnetometer (VSM) measurements show that the remanent magnetization (Mr) of BFC_0.07O (3.6 emu/cm³) and the saturation magnetization (Ms) of BFC_0.10O (48.84 emu/cm³) thin film both increase by approximately two times at room temperature, compared with that of the pure BFO counterpart.