Structural and multiferroic properties of (Sm, Mn) co-doped BiFeO3 materials

Pure BiFeO3 (BFO) and (Sm, Mn) co-doped materials were synthesized by the citrate method. Effects of (Sm, Mn) co-doping on the structural, magnetic, electrical and ferroelectric properties of the BFO materials were characterized and investigated by different techniques, such as X-ray diffraction (XRD), Raman scattering spectroscopy, magnetic hysteresis (M-H) loops, electric polarization hysteresis loops, and complex impedance spectra measurements. Analysis results of the XRD measurement show that all samples were crystallized in the rhombohedral structure with R-3C space group and crystal lattice parameters of a = 0.5584 nm, c = 1.3874 nm and the average crystal size of L-XRD = 60 nm for BFO sample. The crystal lattice parameters a, c and the average crystal size L-XRD of (Sm, Mn) co-doped samples were found to decrease with the increasing Sm concentration. The Raman scattering spectral show that the position of peaks characteristic for the Fe-O bonds in the (Sm, Mn) co-doped samples shifts toward lower frequency compared to that of BFO. For the (Sm, Mn) co-doped samples, the position of peaks characteristic for Bi-O covalent bonds shifts toward higher frequencies when the Sm concentration increases, confirming that Sm3+ and Mn2+ ions are substituted into Bi-sites and Fe-sites, respectively. The data from the magnetic hysteresis loop measurements indicate that all samples exhibit weak ferromagnetic behavior. The BFO sample presents weak ferromagnetic properties with a saturation magnetization of Ms = 0.015 emu/g and the remnant magnetization of Mr = 0.007 emu/g. Ferromagnetic properties of the (Sm, Mn) co-doped samples are found enhanced compared to those of BFO. The origin of ferromagnetism of the materials has been considered.