Phase diagram of Sm and Mn co-doped bismuth ferrite based on crystal structure and magnetic properties

Abstract

Sm and Mn co-substituted BiFeO3 (BFO) ceramic has been synthesized by the tartaric acid modified sol-gel method to understand the effect of structural modification on the magnetic properties. The secondary phases (i.e., Bi2Fe4O9, Bi25FeO39 etc.) present in the parent compound BiFeO3 have been significantly reduced with increase in the substitution percentage of Sm and Mn at Bi and Fe sites of BFO respectively. The Rietveld refinement of the X-ray diffraction (XRD) patterns reveals a structural transition from rhombohedral (R3c, space group) to orthorhombic (Pbnm, space group) crystal symmetry with the concentration of Sm and Mn in the sample. The chemical state and elemental ratio of the samples have been studied by analyzing the X-ray photoelectron spectroscopy (XPS) data. Crystallite size obtained from the transmission electron microscopy analysis is in well comparable with the XRD analysis. Fourier transform infrared spectroscopy (FTIR) analysis supports the XRD results. A change in the phonon frequency and line widths in Raman spectra confirms the lattice distortion in the co-substituted samples which are in agreement with the XRD analysis. Ferromagnetic signature has been observed in Sm and Mn co-substitution. The magnetic hysteresis loop at room temperature has been analyzed by considering both ferromagnetic and antiferromagnetic contribution. The saturation magnetization for ferromagnetic phase increases up to 10% substitution of Sm and Mn in BFO and, decrease with the further increase of percentage of substituents. A correlation between crystal structure and magnetic behavior has been observed for Sm and Mn co-substituted sample. Phase diagram of crystal symmetries percentage, saturation magnetization (MS), remnant magnetization (Mr) and coercivity (HC) of Bi1-xSmxFe1-xMnxO3 for x = 0.000, 0.025, 0.050, 0.075, 0.100 and 0.150 ceramics.