Charge defects and highly enhanced multiferroic properties in Mn and Cu co-doped BiFeO ₃ thin films

Pure BiFeO ₃ (BFO) and Mn, Cu co-doped BiFeO ₃ (BFMCO) thin films were deposited on fluorine doped tin oxide (FTO) substrates by a chemical solution deposition method. Detailed investigations were made on the effects of Mn and Cu co-doping on the crystal structure, the defect chemistry, multiferroic properties of the BFO thin films. With the co-doping of Mn and Cu, a structural transition from the rhombohedral (R3c:H) to the biphasic structure (R3c:H + P1) is confirmed by XRD, Rietveld refinement and Raman analysis. X-ray photolectron spectroscopy (XPS) analysis shows that the coxistence of Fe ²⁺ /Fe ³⁺ and Mn ²⁺ /Mn ³⁺ ions in the co-doping films are demonstrated. Meanwhile, the way of the co-doping at B-sits is conducive to suppress Fe valence state of volatility and to decrease oxygen vacancies and leakage current. It's worth noting that the co-doping can induce the superior ferroelectric properties (a huge remanent polarization, 2P _r ∼ 220 μC/cm ² and a relatively low coercive field, 2E _c ∼ 614 kV/cm). The introduction of Mn ²⁺ and Cu ²⁺ ions optimizes the magnetic properties of BFO thin films by the biphasic structure and the destruction of spin cycloid.