Structural and multiferroic properties of (Sm, Mn) co-doped BiFeO<sub>3</sub> materials

Abstract

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 (<em>M-H</em>) 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 <em>R</em>_3<em>C</em> space group and crystal lattice parameters of <em>a</em> = 0.5584 nm, <em>c</em> = 1.3874 nm and the average crystal size of <em>L</em>_<em>XRD</em> = 60 nm for BFO sample. The crystal lattice parameters <em>a, c</em> and the average crystal size <em>L</em>_<em>XRD</em> 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 <em>Ms</em> = 0.015 emu/g and the remnant magnetization of <em>Mr</em> = 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.