Improved multiferroic properties in (Ho, Mn) co-doped BiFeO₃ thin films prepared by chemical solution deposition

Pure BiFeO₃ (BFO), Bi_0.92Ho_0.08FeO₃ (BHFO) and Bi_0.92Ho_0.08Fe_0.97Mn_0.03O₃ (BHFMO) films were successfully deposited on FTO/glass substrates by chemical solution deposition method. X-ray diffraction, Rietveld refinement and Raman spectra results demonstrate that a structural transition from rhombohedral (R3c:H) to biphasic structure (R3c:H+R-3m:R) occurs in BHFC and BHFMO films. The improved dielectric properties, leakage current, ferroelectric properties and ferromagnetic properties are obtained by co-doping Ho and Mn. A giant remanent polarization (2P_r~231.4 μC/cm²) is observed in BHFMO film. In addition, the dramatically decreased leakage current density (4.02×10^-4 A/cm² at 400 kV/cm) is obtained in BHFMO film, which is about two orders of magnitude lower than that of pure BFO. The superior ferroelectric properties of BHFMO film are mainly attributed to the structure transition and low leakage current. Furthermore, BHFMO film shows enhanced ferromagnetism (M_s~2.74 emu/cm³), implying the collapse of space modulated spin structure by the structural transition.