Effect of Mn substitution-driven structural transition on magnetic and optical properties of multiferroic Bi 0.85 La 0.15 FeO 3 ceramics

Bi 0.85 La 0.15 FeO 3 , a Lanthanum (La) modified form of bismuth ferrite (BFO) crystallizes to crystal structure which is free from any impurity, which improves the multiferroic properties of BFO. To achieve the enhanced multiferroic characteristics, the composition of Bi 0.85 La 0.15 FeO 3 has been optimized with the Mn substitution which increases magnetization more effectively than those of magnetic cations. Therefore, Bi 0.85 La 0.15 Fe 1−x Mn x O 3 polycrystalline samples were synthesized using a tartaric acid modified sol–gel technique for x = 0.000, 0.025, 0.050, and 0.100. The effects of substitution of Mn (non-magnetic in nature) at the Fe site on crystal structure, magnetic properties, and optical properties were then investigated. The formation of crystalline phases was checked by using X-ray diffraction. The structural transition from rhombohedral ( R3c , space group) to orthorhombic ( Pbnm , space group) is strongly supported by the Rietveld refinement of the XRD pattern as well as analysis of Raman spectra. As Mn substitution increases, the intensity of Raman peak at about 650 cm −1 increases as well, indicating an increase in the contribution of orthorhombic phase. Magnetic properties of Bi 0.85 La 0.15 Fe 1−x Mn x O 3 polycrystalline samples were assessed at room temperature. In Bi 0.85 La 0.15 Fe 1−x Mn x O 3 , the Mn substitution at the Fe site produced the highest magnetic moment for x = 0.025. Magnetic hysteresis loops show a substantial change in the magnetization with the increase in Mn substitution. Using the Kubelka–Munk (K–M) function and Tauc plot, the band gap energies of all the samples were calculated from UV–Vis diffuse reflectance spectra and it was observed that the band gap energy decreases with the increase in Mn substitution in Bi 0.85 La 0.15 Fe 1−x Mn x O 3. These findings provide better understanding for tuning of the multiferroic properties of Mn substituted Bi 0.85 La 0.15 FeO 3 ceramics.