Abstract
Zinc ferrite nanoparticles were obtained by chemical methods (co-precipitation and thermal decomposition of metalorganic compounds) and systematically probed with volume (XRD, VSM), microscopic (TEM) and element sensitive probes (ICP-OES, Mössbauer Spectroscopy, XPS, XAFS). Magnetic studies proved the paramagnetic response of stoichiometric ZnFe2O4 (ZF) nanoparticles, while superparamagnetic behavior was observed in as-synthesized, non-stoichiometric ZnxFe3−xO (NZF) nanoparticles. Upon annealing up to 1400 °C in an inert atmosphere, a significant change in the saturation magnetization of NZF nanoparticles was observed, which rose from approximately 50 up to 140 emu/g. We attribute this effect to the redistribution of cations in the spinel lattice and reduction of Fe3+ to Fe2+ during high-temperature treatment. Iron reduction is observed in both ZF and NZF nanoparticles, and it is related to the decomposition of zinc ferrite and associated sublimation of zinc oxide.
Highlights
NANOCRYSTALLINE magnetic nanoparticles are characterized by unique properties, such as superparamagnetism, stable core/shell structures, high catalytic activity and chemical reactivity
Our results show that high temperature thermal treatment of non-stoichiometric ZnxFe3ÀxO (NZF) NPs in inert atmosphere leads to significant Fe3+ reduction and similar structural transformations as in the case of ZF NPs, but magnetic properties are greatly enhanced, contrary to ZF NPs
NZF NPs were synthesized via thermal method, which was redesignated based on the synthesis in References 23, 64–67
Summary
NANOCRYSTALLINE magnetic nanoparticles are characterized by unique properties, such as superparamagnetism, stable core/shell structures, high catalytic activity and chemical reactivity. The authors assume that these changes result from Fe3+ reduction to Fe2+.[45] Singh et al.[48] investigated the influence of temperature (from 400 °C to 700 °C, in air) and sintering time of ZF NPs on the structural and magnetic properties They found that the higher the heating temperature the lower the saturation magnetization of particles. Makovec et al.[22] pointed out that heating of ZF and NZF NPs to a temperature of approximately 600 °C causes significant changes in their lattice parameter and magnetization These changes are related to the change in the nanoparticle composition and structure. Our results show that high temperature thermal treatment of NZF NPs in inert atmosphere leads to significant Fe3+ reduction and similar structural transformations as in the case of ZF NPs, but magnetic properties are greatly enhanced, contrary to ZF NPs
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