Electronic and magnetic properties of transition metal compounds: An x-ray spectroscopic study

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Title: Electronic and magnetic properties of transition metal compounds: An x-ray spectroscopic study
Authors: Küpper, Karsten
Thesis advisor: apl. Prof. Dr. Manfred Neumann
Thesis referee: Prof. Dr. Gunnar Borstel
Abstract: The aim of the present work was to develop a detailed picture of the electronic and magnetic properties of a number of interesting transition metal compounds. A number of complementary experimental and theoretical techniques have been applied, special emphasis was given to x-ray spectroscopies. The studies led to a number of results, and the following conclusions can be drawn: The influence of the magnetic ground state (high-spin (FeO) vs. low-spin (FeS2)) with respect to the recorded x-ray spectra was investigated. In particular, by performing RXES on the Fe L edge of the two compounds, very different ratios of La / Lβ integrated intensity for excitation energies close to the L2 edge have been observed. This effect has been explained in terms of the magnetic structure of FeO (high spin), which inhibits Coster-Kronig processes. Special attention has been given to the direct investigation of orbital ordering in a three dimensional CMR manganite, namely La7/8Sr1/8MnO3, by means of x-ray linear dichroism (XLD). We obtained, for the first time, rather strong indications that the coherently distorted Jahn-Teller phase in La7/8Sr1/8MnO3 is accompanied by a predominantly cross type (x2-z2) / (y2-z2) orbital ordering. In addition to manganites the double perovskite Sr2FeMoO6 the combined study by means of x-ray spectroscopies, magnetic measurements and theoretical band structure calculations could resolve some points discussed controversially in the literature. Both, paramagnetic measurements as well as core level spectroscopy of the Fe 2p, Fe 3s and the Mo 3d states suggest a mixed iron valence state involving around 30% Fe3+- Mo5+ and 70% Fe2+ - Mo6+ states in highly ordered Sr2FeMoO6. XPS valence band studies reveal that the Fe 3d states are not extremely localized, and we find evidence that charge transfer between Fe 3d and O 2p states plays an essential role.
URL: https://repositorium.ub.uni-osnabrueck.de/handle/urn:nbn:de:gbv:700-2005071510
Subject Keywords: electronic structure; colossal magneto resistance; double perovskites; manganites; transition metal compounds
Issue Date: 15-Jul-2005
Type of publication: Dissertation oder Habilitation [doctoralThesis]
Appears in Collections:FB04 - E-Dissertationen

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