Influence of synthesis method on structural and magnetic properties of cobalt ferrite nanoparticles |
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Authors: | Sa?o?Gyergyek Darko?Makovec Alojz?Kodre Iztok?Ar?on Marko?Jagodi? Miha?Drofenik |
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Institution: | (1) “Jozef Stefan” Institute, Ljubljana, Slovenia;(2) Faculty of Mathematics and Physics, University of Ljubljana, Ljubljana, Slovenia;(3) University of Nova Gorica, Nova Gorica, Slovenia;(4) Institute of Mathematics, Physics and Mechanics, Ljubljana, Slovenia;(5) Faculty of Chemistry and Chemical Engineering, University of Maribor, Maribor, Slovenia |
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Abstract: | The Co–ferrite nanoparticles having a relatively uniform size distribution around 8 nm were synthesized by three different
methods. A simple co-precipitation from aqueous solutions and a co-precipitation in an environment of microemulsions are low
temperature methods (50 °C), whereas a thermal decomposition of organo-metallic complexes was performed at elevated temperature
of 290 °C. The X-ray diffractometry (XRD) showed spinel structure, and the high-resolution transmission electron microscopy
(HRTEM) a good crystallinity of all the nanoparticles. Energy-dispersive X-ray spectroscopy (EDS) showed the composition close
to stoichiometric (~CoFe2O4) for both co-precipitated nanoparticles, whereas the nanoparticles prepared by the thermal decomposition were Co-deficient
(~Co0.6Fe2.4O4). The X-ray absorption near-edge structure (XANES) analysis showed Co valence of 2+ in all the samples, Fe valence 3+ in
both co-precipitated samples, but average Fe valence of 2.7+ in the sample synthesized by thermal decomposition. The variations
in cation distribution within the spinel lattice were observed by structural refinement of X-ray absorption fine structure
(EXAFS). Like the bulk CoFe2O4, the nanoparticles synthesized at elevated temperature using thermal decomposition displayed inverse spinel structure with
the Co ions occupying predominantly octahedral lattice sites, whereas co-precipitated samples showed considerable proportion
of cobalt ions occupying tetrahedral sites (nearly 1/3 for the nanoparticles synthesized by co-precipitation from aqueous
solutions and almost 1/4 for the nanoparticles synthesized in microemulsions). Magnetic measurements performed at room temperature
and at 10 K were in good agreement with the nanoparticles’ composition and the cation distribution in their structure. The
presented study clearly shows that the distribution of the cations within the spinel lattice of the ferrite nanoparticles,
and consequently their magnetic properties are strongly affected by the synthesis method used. |
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