Magnetic nanoparticles (NPs) with spinel structure are of potential interest for several fields, as their functionality can be tuned acting on their chemical and physical properties. The magnetic response of Fe@Fe-oxide core@shell NPs, for instance, can be adjusted by a proper balance of core and shell composition , opening the way for innovative biomedical applications. Moreover, the novel magnetic phenomena arising between Fe core and Fe-oxide shell, such as interface spin disorder and exchange bias, make these multicomponent nanoparticles appealing even for fundamental research on magnetism .
A fine characterization of such systems requires physical and chemical properties to be probed together with the effects produced by their interplay. In this respect, inner-shell spectroscopies represent the ideal investigation tool, as they provide element specificity together with sensitivity to oxidation, spin state, and local geometry of the sample: the combination of these pieces of information allows one to assess the coupling between the NPs properties and functionality.
The high photon flux and the wide energy range available at the CLÆSS (Core Level Absorption and Emission Spectroscopies) beamline, combined with the fine resolution provided by the CLEAR spectrometer  were employed to obtain complementary information on the local electronic, magnetic, and structural properties of different NPs made of Fe compounds. Fe K-edge X-ray Emission and high-resolution X-ray Absorption Near Edge Structure Spectroscopies (XES and XANES) were performed on a variety of Fe NPs, including spherical Fe@(Fe3O4+γ-Fe2O3) (15 nm) and Fe3O4@CoFe2O4 (9 nm) core@shell NPs, and FeO+Fe3O4 (28 nm) nanocomposites.
Our data identify different de-excitation channels of Fe atoms: focussing on the Kb'and Kb1,3emission lines, details on the average magnetic moment of Fe in different environments are obtained. High-resolution XANES spectra collected in partial fluorescence yield are spin selective and sensitive to Fe atoms in different coexisting phases/sites on the basis of the Kbenergy regions. The combination of XES and high-resolution XANES brings the possibility to detect differences in the local electronic structure and average environment of Fe atoms in different magnetic states.
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