New insights into the structural analysis of maghemite and (MFe2O4, M = Co, Zn) ferrite nanoparticles synthesized by a microwave-assisted polyol process
a
Aida
Serrano,
cd
Lucía
Gutiérrez,
e
Nieves
Menéndez,
f
María
del Puerto Morales
*a
and
Eva
Mazarío
*af
Abstract
The search for more efficient, scalable, reproducible and standardized synthesis methods able to control particle size and crystallinity is still a challenge in nanotechnology. The one-pot microwave-assisted polyol process has been optimized for the synthesis of well-defined ferrite nanoparticles. Highly uniform and crystalline γ-Fe2O3, CoFe2O4 and ZnFe2O4 nanoparticles, with diameters below 14 nm have been prepared by an easy and reproducible one-pot microwave-assisted heating procedure in a polyol medium. A pure single phase and cubic spinel structure were confirmed by powder X-ray diffraction and Raman spectroscopy. Depending on the metal precursors, nanoparticles display magnetic features from superparamagnetic behaviour (Fe- and Zn-ferrites) to ferrimagnetism (Co ferrite) at room temperature. The iron oxidation state of 3+ and its short-range order coordination were studied by XAS (X-ray absorption spectroscopy). External field Mössbauer spectra, recorded at low temperature, confirmed the ferrimagnetic order with a Fe3+ and M2+ partial cationic distribution within both the A and B sites in zinc and cobalt ferrite, respectively. According to these results, the ferrite stoichiometry was (Zn0.70Fe0.30)[Zn0.30Fe1.70]O4 and (Co0.28Fe0.72)[Co0.72Fe1.28]O4.
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