Structural, physical, and magnetic properties of nanocrystalline manganese-substituted lithium ferrite synthesized by sol-gel autocombustion technique

Nanoparticles of spinel ferrite Li0.5-0.5xMnxFe2.5-0.5xO4 (x=0, 0.25, 0.5, 0.75 and 1) were prepared by sol-gel autocombustion technique. The crystalline phase formation, morphology, cation distribution, and magnetic properties of Li0.5-0.5xMnxFe2.5-0.5xO4 nanoferrite samples were investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), infrared (IR) spectroscopy, and vibrating sample magnetometer (VSM). The lattice parameter increases by Mn substitution, while both the crystallite size and Curie temperature (T-C) decrease. Values for both the saturation magnetization (M-s) and the coercivity (H-c) were enhanced because both are larger for Mn-substituted samples than those for unsubstituted ones. The addition of Mn2+ ions promotes (M-s) until (x=0.5) then an appreciable decrease occurs, whereas the coercivity (H-c) increases up to x=0.25 then it decreases. The role of the substitution with Mn2+ ions in changing all investigated properties of lithium ferrite was explained according to different theories.