Abstract
MIIFe2O4 (M = Fe, Zn) electric double layer ferrofluids (edl-ferrofluids) were investigated and characterized by Raman micro-spectroscopy as solids (powder) or in solution forming magnetic fluids. The Raman spectra showed that the nanoparticles forming the magnetic fluids have different compositions depending on the MII ion used in their preparation. In the case of FeFe2O4 edl-ferrofluid, maghemite, magnetite, an amorphous non-stoichiometric oxyhydroxide [FeOx(OH)3 − 2x, x<1] and Fe(OH)3 phases are present. In the case of the ZnFe2O4 edl-ferrofluid, a magnetite-like structure where the FeII centers were replaced by the ZnII ions is present. A model of the distribution of the different chemical phases on the nanoparticles is presented. The Raman spectrum of the FeFe2O4 edl-ferrofluid excited close to an absorption band of the sample at 650 nm presents several Raman features above 900 cm−1 that are not observed for the ZnFe2O4 edl-ferrofluid sample. These results have been interpreted considering the resonant excitation of the density of phonon states with k ≠ 0 due to quantum size effects. Copyright © 2000 John Wiley & Sons, Ltd.
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