Effect of Cr doping on the phase structure, surface appearance and magnetic property of BiFeO₃ thin films prepared via sol–gel technology

Multiferroic BiFeO₃ (BFO) and BiFe_1−xCr_xO₃ (BF_1−xC_xO, x = 0.05, 0.1, 0.15 and 0.2) thin films were successfully synthesized on silicon (111) substrates via sol–gel technology. The effect of Cr³⁺ ion doping on the phase structure, surface morphology, valence states for Fe element and magnetic property was investigated. The introduction for simulation images of ionic space arrangement was to better comprehend the substitution site and superexchange interaction between the Fe³⁺ (Cr³⁺) and O²⁻ ions. The phase structure of Cr-doping thin films transition from rhombohedral to orthorhombic was confirmed by the X-ray diffraction (XRD) and Raman measurements, and the obtained results also demonstrated that the Cr³⁺ ions successfully located in Fe²⁺ and Fe³⁺ ions sites of BFO lattice system. The Field Emission Scanning Electron Microscopy (FESEM) patterns clearly exhibited that the grains sizes were remarkably decreased by Cr³⁺ ions doping, and the surfaces textures got glossier and smoother judging from the Atomic Force Microscope (AFM) images. The dense surface structure can restrict the O²⁻ ions escaping from the lattices system, which is beneficial for the release of magnetic property due to superexchange interaction of improvement. It was found that the saturation magnetization (Ms) was significantly linearly increased accompanying the adding of Cr-doping due to destroying of spatial modulation helical structure and enhancing of superexchange interaction. Moreover, the Hall-effect results firstly revealed that the carrier concentration and mobility rate played significant roles in magnetoelectric effect behaviors.