Study on the multiferroic properties of 2-2 type of BiFeO3-CuFe2O4 thin films

The 2-2 type BiFeO3-CuFe2O4(BFO-CFO) bilayer thin films were deposited on FTO/glass substrates by sol-gel method, using Bi(NO3)3·5H2O, Fe(NO3)3·9H2O and Cu(NO3)3·3H2O as the raw materials. The structure, surface morphologies and electric properties of the thin films were investigated. The XRD patterns show that the structure of BFO is the distorted rhombohedral perovskite with R3c:H (161) space lattice, CFO is the tetragonal spinel with type I41/amd (141) space lattice. The interface is obvious between the CFO and BFO films, which shows that the BFO and CFO have no inter-diffusion phenomena. When the frequency is 10 kHz, the dielectric loss peak is consistent with the dielectric relaxation of Wagner Maxwell. The leakage current density of BFO-CFO under positive and negative bias voltages is asymmetric, and there is a hysteresis phenomenon in the positive bias voltage. The results of XPS show that the Fe2+ of the BFO-CFO is decreased and the leakage current of the film is improved. The saturation magnetization (Ms) of BFO-CFO is 25.8 emu/cm3 at room temperature, which is about 40 times of the pure BFO.