hossein asnaashari eivari

Superparamagnetic nanoparticles with high saturation magnetism and small average size were synthesized by the economic co-precipitation method. FeCl2.4H2O and FeCl3.6H2O were used as salt agents and NaOH as precipitant. Different reaction conditions were investigated to improve the saturation magnetization of synthesized magnetic nanoparticles by adjusting the reactants' concentration and the reaction's temperature. The magnetic and structural properties of the synthesized nanoparticles were investigated by XRD and VSM, respectively. Magnetization curves were analyzed to calculate the size of the magnetic moment of nanoparticles and saturation magnetization. For each sample, three mean magnetic sizes were estimated by employing the region of the curve in the small limit, high limit, and both small and high limits of applied magnetic fields. Their sizes were also estimated by using the Scherrer formula. The mean magnetic size estimated using the region of small applied fields was in agreement with that estimated by the Scherrer formula. Although both saturation magnetization and the size of prepared nanoparticles were increased with reaction temperature, the saturation magnetization of nanoparticles was enhanced from 56 to 85 emu/g. In contrast, their mean magnetic size changed only between 7 to 12 nm.

Electronic structure of various structures of TiO2 were calculated using PBE and HSE06 functionals. Calculated band gap in HSE06 level for rutile and anatase phases was 3.4 and 3.58 eV respectively which are in agreement with experimental values of 3 and 3.2 eV. Calculated bulk moduli for the mentioned phases were to be 226 and 205 Gpa. The difference of these values with reported experimental values are %7 and %14 respectively. Comparison between the two mentioned functionals shows that the overall form of band structures is independent of the functional. Especially the top of valence band and the bottom of conduction band are the same in PBE and HSE06. So both functionals give the same result for the type (direct or indirect) of band-gap. Distance between conduction and valence bands, and so the band-gap, is the main difference in calculating the band-structure using these two functionals. Band-gap difference calculated by these functionals is almost 1.6 eV for all structures studied in here. So one can calculate the band-gap of TiO2 with PBE and sum the result by 1.6 eV instead of calculating the band gap in expensive HSE06 level which is close to experimental value.