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The compound NiCo 2 O 4 , with spinel-related structure, has been prepared by thermal decomposition of metal nitrates and its bulk structural properties examined by means of magnetic measurements, neutron diffraction, X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS). The results suggest a delocalised electron distribution on the octahedral sites with average oxidation states of z3.5 and z2.5 for nickel and cobalt, respectively, and lead to a cation distribution for NiCo 2 O 4 of {Ni 3z 0.1 Co 2z 0.9 } tet [Ni 3.5z 0.9 Co 2.5z 1.1 ] oct O 4 . This electronic configuration is consistent with magnetisation measurements if applied magnetic fields cause a charge redistribution on the octahedral sites to favour Co 3z and Ni 3z . The surface of NiCo 2 O 4 was examined by X-ray photoelectron spectroscopy (XPS) and found to have a different composition containing Co 2z , Co 3z , Ni 2z , Ni 3z and, probably, Ni 4z .

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Abstract. 57Fe transmission Mossbauer at temperatures between 18 and 298 K and magnetic measurements have been used to characterize Fe-filled carbon nanotubes which were prepared by pyrolisis of Ferrocene + C60 at atmospheric pressure under an Ar atmosphere at 1050°C. The Mossbauer data have shown that the Fe phase s encapsulated within the carbon nanotubes are a-Fe, Fe3C and y-Fe. The magnetic results are compatible with the Mossbauer data . Taken together the results allow us to propose a simple picture of the distribution of iron phases within the carbon nanotubes which would consist of an a-Fe core surrounded by an y-Fe shell, finally covered by an Fe3C layer.

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