Use of Raman micro-spectroscopy in the characterization of M(II)Fe2O4 (M =Fe, Zn) electric double layer ferrofluids

(MFe2O4)-Fe-II (M = Fe, Zn) electric double layer ferrofluids (edl-ferroflu ids) were investigated and characterized by Raman micro-spectroscopy as sol ids (powder) or in solution forming magnetic fluids. The Raman spectra show ed that the nanoparticles forming the magnetic fluids have different compos itions depending on the Mn ion used in their preparation. In the case of Fe Fe2O4 edl-ferrofluid, maghemite, magnetite, an amorphous non-stoichiometric oxyhydroxide FeOx(OH)(3-2x), x < 1] and Fe(OH)(3) phases are present. In t he case of the ZnFe2O4 edl-ferrofluid, a magnetite-like structure where the Fen centers were replaced by the Zn-II ions is present. A model of the dis tribution of the different chemical phases on the nanoparticles is presente d. The Raman spectrum of the FeFe2O4 edl-ferrofluid excited close to an abs orption band of the sample at 650 mm presents several Raman features above 900 cm(-1) that are not observed for the ZnFe2O4 edl-ferrofluid sample. The se results have been interpreted considering the resonant excitation of the density of phonon states with k not equal 0 due to quantum size effects. C opyright (C) 2000 John Whey & Sons, Ltd.