Preparation and characterization of nanosized magnesium ferrite powders by a starch-gel process and corresponding ceramics

The synthesis and characterization of nano-sized MgFe2O4 by a starch-gel methodis described herein. A phase-pure nano-sized MgFe2O4 powder (1a) was obtained aftercalcining a (MgFe)-starch gel at 550 °C. The powder has a specific surface area of 60.6 m2/gand a crystallite size of 9 nm. TEM investigations reveal particles in the range of 7 to 15 nm.The activation energy of the crystallite growth process was calculated as 89 ± 14 kJ/mol. Theshrinkage and sintering behaviour of resulting compacts were studied. UV−VIS investigationsof the nano-sized powder 1a reveal an optical band gap of 2.38 eV, whereas calcination at1100 °C (powder 1g) leads to a crystallite size of 129 nm and a band gap of 2.16 eV.Magnetization loops at 300 K and the temperature dependence of both the field-cooled (FC) and the zero-field-cooled (ZFC) magnetization indicate a superparamagnetic behaviour. The blocking temperature for powder 1a was determined as 140 K at a field of H = 500 Oe. Wefound different saturation magnetizations (Ms) depending on the calcination temperature. Calcination at 550 °C (1a) results in Ms = 20.0 emu/g which increases with calcinationtemperature to a maximum of 37.7 emu/g for powder 1e calcined at 900 °C. Ceramic bodiessintered between 1450 and 1600 °C exhibit Ms values of 25−28 emu/g. Magnetic investigations at 10 K on powders 1a−1g show hysteresis loops with coercivities up to 950Oe, remanences to 10 emu/g and Ms values to 50.4 emu/g. Additionally, the nano-scaled powders show a shift of the hysteresis loops.