Thermolysis studies on magnesium zinc bis(citrato)ferrate pentahydrate precursor for synthesis of ferrite nanoparticles

Thermolysis of magnesium zinc bis(citrato) ferrate pentahydrate, MgZn2[Fe(C6H5O7)2]25H2O, has been investigated from ambient to 600 °C employing various physico-chemical techniques viz. TG–DTG–DSC, IR, XRD and Mössbauer spectroscopy for the characterization of intermediates and final thermolysis products. Dehydration of the precursor completes at 140 °C followed by abrupt exothermic decomposition to yield α-Fe2O3, ZnO and MgO as intermediate oxide phases. Finally solid state reaction between oxides results in the formation of spinel ferrite Mg0.3Zn0.7Fe2O4 as the final thermolysis product at a temperature (350 °C) much lower than for the ammonium substituted citrate precursor (540 °C) and conventional ceramic method (1350 °C). Monodispersed and nanosized nature of ferrite with average particle diameter of 35 nm is confirmed by transmission electron microscopy (TEM). The Mössbauer spectrum of the final thermolysis product displays a doublet owing to the presence of superparamagnetism (SPM) at room temperature. SPM in multi-domain particles is attributed to weakening of A–B exchange interactions, resulting in lowering of anisotropic energy which facilitates onset of SPM at room temperature. Thermolysis pattern has been compared with pure magnesium ferricitrate and ammonium substituted ferricitrate.