Cation distribution and magnetic structure of the ferrimagnetic spinel NiCo2O4

José F. Marco, J. Ramón Gancedo, Mercedes Gracia, Juan Luis Gautier, Edmundo I. Ríos, Helen M. Palmer, Colin Greaves, Frank J. Berry

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The compound NiCo2O4, 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 +3.5 and +2.5 for nickel and cobalt, respectively, and lead to a cation distribution for NiCo2O4 of (Ni3+0.1Co2+0.9)tet [Ni3.5+0.9Co2.5+1.1] octO4. This electronic configuration is consistent with magnetisation measurements if applied magnetic fields cause a charge redistribution on the octahedral sites to favour Co3+ and Ni3+. The surface of NiCo2O4 was examined by X-ray photoelectron spectroscopy (XPS) and found to have a different composition containing Co2+, Co3+, Ni2+, Ni3+ and, probably, Ni4+.

Original languageEnglish
Pages (from-to)3087-3093
Number of pages7
JournalJournal of Materials Chemistry
Issue number12
Publication statusPublished - 2001

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