Unlocking the hidden potential: exploring the fascinating properties of CoFe2O4@SiO2 nanocomposites driven by annealing
Résumé
A study of the influence of multistage annealing on the properties of CoFe2O4@SiO2 (CFO@SiO2) core-shell nanoparticles synthesized by co-precipitation followed by microemulsion is discussed. The cubic inverse spinel ferrite crystal structure with Fe3+ and Co2+ cation distribution in the A-tetrahedral and B-octahedral sites is confirmed in all analyzed nanocomposites. The structural characterization revealed the subtle temperature-driven CFO core crystallization to about 13 nm. Concurrently, the silica shell exhibits stability regardless of the sample processing. The interplay between larger multi-domain CFO and smaller superparamagnetic (SPM) CFO single-domains is confirmed by the performance of magnetic properties and Mössbauer spectrometry. The spin-canting phenomenon on the CFO surface magnetic dead layer (MDL) is exposed by employing the Yafet-Kittel model. The X-ray photoemission (XPS) and absorption spectroscopy (XAS) studies confirmed the complex nature of the Fe and Co states. The Fe3+ and Co2+ distribution in the crystal lattice is verified by XPS and XAS spectra. The Si-O-Ni/Fe intermixing on the CFO / SiO2 interface is validated by the core-level line analysis, proving the existence of a disordered layer MDL on the CFO surface.
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