2008 NSTI Nanotechnology Conference and Trade Show - Nanotech 2008 - 11th Annual

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Clean Technology 2008

Nanostructured thin layers of vanadium oxides doped with cobalt, prepared by pulsed laser ablation: structure, chemistry, morphology, and magnetism

C.M. Teodorescu, G. Socol, C. Negrila, D. Luca, D. Macovei
National Institute of Materials Physics, RO

Keywords:
diluted magnetic semiconductors, metal-insulator transition, thin magnetic layers

Abstract:
The present study deals with cobalt-doped vanadium oxide thin layers prepared by pulsed laser ablation. Variation of the preparation parameters allows one to synthesize films with a variety of properties. The chemical composition of the films was determined by XPS, the local atomic order by EXAFS and by XANES, the morphology of the films was investigated by AFM, and magnetic properties were quantified by magneto-optical Kerr effect. The chemical composition of the host matrix was found to be the vanadium (5+) oxide, with Co ions either in high ionization state Co5+ (Class A samples) or with Co in lower ionization states Co4+ or Co3+ (Class B). Consistent information was obtained from chemical shifts in XPS and from the amplitude of the pre-edge peak in XANES, whose amplitude is proportional to the number of 3d vacancies per atom. AFM revealed big particles with sizes > 100 microns for Class A samples, whereas smaller nanoparticles with sizes ranging between 20 and 30 microns were observed for Class B samples. Class A samples presented very high coercitive fields with low saturation magnetisation at room temperature, whereas Class B samples presented double-loop hysteresis curves, indicating the coexistence of exchange bias with strong anisotropy.


Nanotech 2008 Conference Program Abstract