Regensburg 2007 – wissenschaftliches Programm

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MA: Fachverband Magnetismus

MA 15: Poster:ThinFilms(1-33),Transp.(34-49),ExchBias(50-56),
Spindynamics(57-70),Micro-nanostr.Mat.(71-82),
Particles/Clust.(83-88), Mag.Imag./Surface(89-96),
Spinelectronics(97-109), Theory/Micromag.(110-116),
Spinstruct/Phasetr.(117-128),Magn.Mat.(129-139),
Aniso.+Measuring(140-145), MolMag.(146-152),
MSMA(153-156)

MA 15.136: Poster

Dienstag, 27. März 2007, 15:00–19:00, Poster A

Investigation of the valence states of Fe_1−xCu_xCr₂S₄ by X-ray absorption spectroscopy — •C. Taubitz¹, M. Raekers¹, V. Tsurkan², and M. Neumann¹ — ¹Universität Osnabrück, Fachbereich Physik, Barbarastraße 7, D-49069 Osnabrück, Germany — ²Institute of Applied Physics, Academy of Sciences 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. A long-standing issue in the attempt to understand the magnetic and electric properties of these compounds has been the Fe valency. We have investigated the valency of Fe by XAS and XPS. 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. While Mössbauer measurements confirm this model our investigations with XAS and XPS show Fe in a divalent state. We suppose that this is due to charge transfer effects between Fe and the S ligand, that originate from the excitation of electrons during the measurement. XPS and XAS measurements of the region 0.5<x<1 show a mixed Fe valence state. We discuss the valence states in comparison with the models of Lotgering and Goodenough.