COMPARATIVE STUDY OF THE STRUCTURE OF BARE MFE2O4 (M = CO, MN) MAGNETIC NANOPARTICLES INVESTIGATED BY NEUTRON DIFFRACTION AND SYNCHROTRON RADIATION

We led a comparative study of the structural properties of CoFe2O4 and MnFe2O4 ferrite nanoparticles (NPs) by combining several experimental techniques such as atomic absorption spectroscopy, induced coupled plasma atomic emission spectroscopy, neutron power diffraction and synchrotron radiation techniques: X-ray absorption spectroscopy and X-ray power diffraction. Divalent molar fraction measurements show that the material synthesized is stoichiometric and XRD results reveal a Jacobsite spinel-structure for both cobalt and manganese ferrite nanoparticles. However, the cation distribution appears to present strong dependence on the cation type, and also on the synthesis process. Rietveld refinements of diffraction data reveal a non-equilibrium inversion degree of 0.65 for the cobalt ferrite NPs and 0.667 for the MnFe2O4 nanoparticles. We found that the valence state of iron cations in the structure of both samples was not affected by the synthesis process, however it was strong enough to oxidize the Mn cations exposing a manganese ferrite structure well described with a mixed valence states of Mn2+, Mn3+ and Mn4+ cations. Due the oxidation of Mn cations in MnFe2O4 NPs, the Mn-O bonds found were smaller when compared to the bulk structure. No changes in the oxidation states of cobalt ions nor in the interatomic distances was found for cobalt ferrite NPs.