Results of a XAS study of new magnetic nanoparticle materials based on iron metal and iron oxides are presented. The materials have potential biomedical applications, e.g. as contrast agents in MRI. Several samples of carbon- silica- and zeolite coated nanoparticles have been obtained by ball milling, arc melting and co-precipitation techniques. The coatings prevent agglomeration of the particles, slow down their removal from the circulation in blood and limit absorption of the harmfull transition elements. In order to determine the local structure and the Fe valence state in the materials, the X-ray absorption spectroscopy in the XANES (X-ray Absorption Near Edge Structure) range was used. The experiments were performed at the Fe:K edge at room temperature in Hasylab/DESY, Hamburg. Metallic Fe, hematite, maghemite and magnetite were used as standards. The edge energy and shape of the spectra of the materials prepared by coprecipitation and milling of magnetite are the closest to those of maghemite. This reveals the oxidation occurring during the preparation procedure. No noticeable difference is observed between the co-precipitated materials annealed in air and argon atmosphere. The results show that the standard characterization of nanomaterials using X-ray diffraction is not sufficient as it does not provide information on the real stoichiometry of iron oxide. The edge energy and shape of the spectra of the nanoparticles prepared by the arc melting of the magnetite filled graphite electrodes are similar to those of metallic iron, which reveals a reduction of magnetite to iron. This fact can be explained by the reducing effect of carbon during melting of magnetite. Preliminary MRI experiments performed on water suspensions of the materials studied indicate their high efficiency in decreasing the T₂ and T₂^* relaxation times.

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