Physical properties of the solid solution NiFe2-xMnxO4 prepared by sol gel

The solid solution NiFe2-xMnxO4 (0 ≤ x ≤ 2) is synthesized by sol gel method and the physical properties are investigated for the first time. The thermal analysis shows that the phases are formed above 400 °C. The oxides crystallize in an inverse cubic spinel whose lattice constant (a: 0.83381–0.83985 nm) increases only slightly up to x = 1.6, according to the Vegard’s law; such result is supported by the FTIR spectra. The UV-Visible spectroscopy shows both direct (1.00–1.56 eV) and indirect optical transitions (0.39–1.65 eV) due to the crystal field splitting of 3d metal. Field-dependent magnetization of the solid solution was measured at 300 K in the region (±20 kOe) and the end member NiFe2O4 exhibits a high magnetism with a saturation magnetization (20 emu/g), comparable to that reported previously. The saturation magnetization varies between 0.5 and 20 emu/g while the coactivity fluctuates between 110 and 239 Oe. The thermal variation of the electrical conductivity indicates a conduction mechanism by low polaron hopping which follows an exponential law with variable activation energies (Ea: 0.12–033 eV). The thermo-power is positive and nearly constant (S300K: 144–130 µVK−1), indicating p type conduction with a mobility more a less constant (1.5–8 × 10−6 V2 cm−1 s−1). The hole densities (NA × 1016: 0.26–2.17) are determined electrochemically from the capacitances measurements in neutral medium (Na2SO4 0.5 M). The flat band potential (Efb: −0.04 to −0.29 V) does not change significantly indicating that the valence band derives mostly from 3d orbital.