Co on Fe3O4(001): Towards precise control of surface properties

R. Gargallo-Caballero, L. Martín-García, A. Quesada, C. Granados-Miralles, M. Foerster, L. Aballe, R. Bliem, G. S. Parkinson, P. Blaha, J. F. Marco, J. de la Figuera

Instituto de Química Física "Rocasolano," CSIC, Madrid E-28006, Spain
Instituto de Cerámica y Vidrio, CSIC, Madrid E-28049, Spain
Department of Chemistry, Aarhus University, Langelandsgade 140, Århus DK-8000, Denmark
ALBA Synchrotron, CELLS, Barcelona, E-08290, Spain
Institut für Angewandte Physik, TU Wien, 1040 Wien, Austria
Institute of Materials Chemistry, TU Wien, 1060 Wien, Austria

J. Chem. Phys. 144 (2016) 094704

A novel approach to incorporate cobalt atoms into a magnetite single crystal is demonstrated by a combination of x-ray spectro-microscopy, low-energy electron diffraction, and density-functional theory calculations. Co is deposited at room temperature on the reconstructed magnetite (001) surface filling first the subsurface octahedral vacancies and then occupying adatom sites on the surface. Progressive annealing treatments at temperatures up to 733 K diffuse the Co atoms into deeper crystal positions, mainly into octahedral ones with a marked inversion level. The oxidation state, coordination, and magnetic moments of the cobalt atoms are followed from their adsorption to their final incorporation into the bulk, mostly as octahedral Co2+. This precise control of the near-surface Co atoms location opens up the way to accurately tune the surface physical and magnetic properties of mixed spinel oxides.

Corresponding author: Juan de la Figuera. Reprints also available from Gareth S. Parkinson (parkinson at iap_tuwien_ac_at).

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