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MA: Fachverband Magnetismus

MA 13: Poster Ia: Electron Theory (1); Magnetic Imaging (2,3); Thin Films (4-25); MSMA (26-33); Magn. Semiconductors (34-42); Magn. Half Metals and Oxides (43-60)

MA 13.38: Poster

Dienstag, 24. März 2009, 10:15–13:00, P1A

Investigation of the valence states of Fe_1−xCu_xCr₂S₄ by photoelectron spectroscopy — •Christian Taubitz¹, Michael Raekers¹, Vladimir Tsurkan², and Manfred Neumann¹ — ¹Universität Osnabrück, Fachbereich Physik, Barbarastraße 7, D-49069 Osnabrück, Germany — ²Institute of Applied Physics, Academy of Science of Moldova, Kishinev MD 2028, Republic of Moldova

Spinel compounds of Fe_1−xCu_xCr₂S₄ have attracted much attention since the discovery of a very large negative magnetoresistance (MR) effect. The valencies of Fe, Cu and Cr have been a long-standing issue in the attempt to understand the magnetic and electric properties of these compounds. In the region 0≤x≤0.5 the Lotgering model predicts Fe to be in a mixed valence state between Fe²⁺ and Fe³⁺. For x=0.5 all Fe-ions are assumed to be trivalent. Mössbauer measurements confirm this model, however investigations with XAS and XPS show Fe to stay in a divalent state for 0≤x≤0.5. We show XAS, XPS and XMCD measurements of single crystalline Fe_0.5Cu_0.5Cr₂S₄ and the first XPS measurements of Fe_1−xCu_xCr₂S₄ single crystals for x>0.5. Our results indicate no ion valency change to be present in Fe_1−xCu_xCr₂S₄ over the whole Cu concentration range. When the surface of Fe_0.5Cu_0.5Cr₂S₄ is oxidised we find Fe³⁺ in a paramagnetic state. We discuss our results in view of Mössbauer measurements and theoretic models, and give possible explanations for the contradictory results.