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

• Published in: Journal of materials science 2013-10, Vol.48 (19), p.6509-6518
• Main Authors: Köferstein, Roberto, Walther, Till, Hesse, Dietrich, Ebbinghaus, Stefan G.
• Format: Article
• Language: English
• Subjects: Calcination; Ceramic materials; Ceramic powders; Ceramics; Characterization and Evaluation of Materials; Chemical properties; Chemical Sciences; Chemistry and Materials Science; Classical Mechanics; Compacts; Crystallites; Crystallography and Scattering Methods; Energy gap; Hysteresis loops; Inorganic chemistry; Iron compounds; Magnesium ferrites; Magnetization; Material chemistry; Materials Science; Nanocomposites; Nanomaterials; Nanostructure; Polymer Sciences; Roasting; Shrinkage; Sintering; Sintering (powder metallurgy); Solid Mechanics; Temperature dependence
• ISSN: 0022-2461; 1573-4803
• DOI: 10.1007/s10853-013-7447-x

The synthesis and characterization of nanosized MgFe 2 O 4 by a starch-gel method is described herein. A phase-pure nanosized MgFe 2 O 4 powder ( 1a ) was obtained after calcining a (MgFe)-starch gel at 550 °C. The powder has a specific surface area of 60.6 m 2 /g and a crystallite size of 9 nm. TEM investigations reveal particles in the range of 7–15 nm. The activation energy of the crystallite growth process was calculated as 89 ± 14 kJ/mol. The shrinkage and sintering behaviour of resulting compacts were studied. UV–Vis investigations of the nanosized powder 1a reveal an optical band gap of 2.38 eV, whereas calcination at 1100 °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 and the zero-field-cooled magnetization indicate a superparamagnetic behaviour. The blocking temperature for powder 1a was determined as 140 K at a field of H  = 500 Oe. We found different saturation magnetizations ( M s ) depending on the calcination temperature. Calcination at 550 °C ( 1a ) results in M s  = 20.0 emu/g which increases with calcination temperature to a maximum of 37.7 emu/g for powder 1e calcined at 900 °C. Ceramic bodies sintered between 1450 and 1600 °C exhibit M s values of 25–28 emu/g. Magnetic investigations at 10 K on powders 1a – 1g show hysteresis loops with coercivities up to 950 Oe, remanences to 10 emu/g and M s values to 50.4 emu/g. Additionally, the nanoscaled powders show a shift of the hysteresis loops.