Use of Raman micro-spectroscopy in the characterization of MIIFe2O4 (M = Fe, Zn) electric double layer ferrofluids

Abstract

M II Fe 2 O 4 (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 M II ion used in their preparation. In the case of FeFe 2 O 4 edl-ferrofluid, maghemite, magnetite, an amorphous non-stoichiometric oxyhydroxide [FeO x (OH) 3−2x , x < 1] and Fe(OH) 3 phases are present. In the case of the ZnFe 2 O 4 edl-ferrofluid, a magnetite-like structure where the Fe II centers were replaced by the Zn II ions is present. A model of the distribution of the different chemical phases on the nanoparticles is presented. The Raman spectrum of the FeFe 2 O 4 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 ZnFe 2 O 4 edl-ferrofluid sample. These results have been interpreted considering the resonant excitation of the density of phonon states with k 6 = 0 due to quantum size effects.

Microstructure and magnetic properties of MFe2O4 (M = Co, Ni, and Mn) ferrite nanocrystals prepared using colloid mill and hydrothermal method

“…Additionally, owing to the occurrence of the peak at about 1300 cm À1 , Raman spectra further confirm that Fe 2 O 3 phase exists in NiFe 2 O 4 ferrite nanocrystals, which is in good agreement with the conclusion obtained from the XRD patterns. 16 Fig . 4 depicts the magnetic hysteresis loops collected at room temperature for the as-synthesized samples.…”

Raman spectroscopy investigation of magnetite nanoparticles in ferrofluids

“…Other possible iron oxide or hydroxide that could have contribution in this region, when considering magnetite nanoparticles, is non-stoichiometric goethite (a-FeOOH) [23] with its high intensity peak situated at 385 cm À 1 . The fact that we probe directly a water suspension lead us to the assumption that the 385 cm À 1 contribution, seen in both 4.63 mW spectra, is due to some [OH] À groups linked with Fe 3 + situated on magnetite's surface, resulting in non-stoichiometric goethite-like structure.…”

Raman study of NiFe2O4 nanoparticles, bulk and films: effect of laser power

“…[15] The spectra match well with those Fe 3 O 4 exhibiting a similar structure. [16] However, the Raman bands of Fe 3 O 4 are sharper and well defined, whereas in the case of NiFe 2 O 4 the Raman bands ( Fig. 2(a)) showed a shoulder-like feature at the lower wavenumber side of all the Raman active bands.…”