Available on-demand - F.SF01.07.03
ZnxFe3-xO4 Nanoparticles—Structural and Magnetic Behaviour Evolution After Thermal Treatment up to 1400 oC
Angelika Kmita1,Jan Zukrowski1,Juliusz Kuciakowski1,2,Marianna Marciszko-Wiackowska1,Antoni Zywczak1,Dorota Lachowicz1,Marta Gajewska1,Marcin Sikora1
AGH University of Science and Technology, Academic Centre for Materials and Nanotechnology1,AGH University of Science and Technology,Faculty of Physics and Applied Computer Science2
Zinc ferrite nanoparticles are currently of much interest for their potential applications in extreme conditions like high temperature: e.g. in metal casting, in water splitting reaction for H2 production (solar fuels) or as high - temperature desulfurizing sorbents [1-3]. Bulk ZnFe2O4 (ZF) should have paramagnetic nature around room temperature, when it is the normal spinel with Zn2+ incorporated mostly in the tetrahedral lattice sites. In the case of nanoparticles, the situation is more complex due to high probability of inversion in the cation distribution between octahedral and tetrahedral sites, which may lead to ferrimagnetism or superparamagnetism [4-6]. It was suggested that during heating Zn2+ ions can move from tetrahedral site to octahedral site whereas Fe3+ ions redistribute within the octahedral and tetrahedral sites in order to reduce the strain . It was also speculated the possibility of reduction of Fe3+ to Fe2+ during high temperature treatment. In order to verify these hypotheses we have performed a comprehensive study of structural and magnetic properties of stoichiometric and non-stoichiometric zinc ferrite ZnxFe3-xO4 (NZF) nanoparticles synthesized using co-precipitation and thermal decomposition method [2, 8] as well as their evolution after thermal treatment. Nanoparticles with different zinc to iron ratio were obtained and systematically probed with volume (XRD, VSM, TG/DSC), microscopic (TEM) and element sensitive probes (ICP-OES, Mossbauer spectroscopy, XPS, XAFS). Magnetic studies proved paramagnetic response of stoichiometric ZF nanoparticles, while a superparamagnetic behaviour is observed in strongly non-stoichiometric (as synthesized) nanoparticles. After thermal treatment at 1400 oC in inert atmosphere, significant changes in the saturation magnetization were observed in the case of NZF. This is related with an increase of the amount of formally Fe2+ ions. The estimated saturation magnetization of as synthesized NZF nanoparticles, of approx. 50 emu/g, is increased upon thermal treatment (at 1400 oC in inert atmosphere) up to approx. 130 emu/g. As such we have confirmed that zinc concentration and method of synthesis plays important role in magnetic properties of non-stoichiometric zinc ferrite nanoparticles. Moreover, the reduction of Fe3+ to Fe2+ during high temperature treatment has been observed in NZF nanoparticles annealed in inert atmosphere.
Acknowledgements: This work was supported by the National Science Centre, Poland, Grant No: 2016/23/D/ST8/00013.
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