An x-ray spectroscopic study of novel materials for electronic applications

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Titel: An x-ray spectroscopic study of novel materials for electronic applications
Autor(en): Raekers, Michael
Erstgutachter: apl. Prof. Prof. h.c. Dr. Dr. h.c. Manfred Neumann
Zweitgutachter: Prof. Dr. Gunnar Borstel
Zusammenfassung: The electronic and magnetic structure of the colossal magneto resistance material La1-xSrxMnO3, the high-k and strain tailoring compounds REScO3 (Sm, Gd, Dy) and the multiferroic LuFe2O4 was investigated by means of x-ray spectroscopic techniques. SQUID measurements of La1-xSrxMnO3 (x = 0.125, 0.17, 0.36) were compared with XMCD results. The very good agreement between these two experiments proofs the applicability of the correction factor for the spin magnetic moment and the importance of charge transfer. The magnetic moment measured by SQUID and that determined from XMCD proofs that the magnetic moment is completely localized at the Mn ions for different temperatures and magnetic fields. For x = 0.125 the orbital magnetic moment determined from XMCD corresponds to the structural changes in the phase diagram. Additionally the measured orbital moments correspond to anomalies in magnetization versus temperature curves. The magnetic and electronic structure of the rare earth scandates (SmScO3, GdScO3 and DyScO3) were investigated by means of XPS, XES, XAS, SQUID and neutron powder diffraction. The magnetic measurements reveal antiferromagnetic coupling at low temperatures in agreement with neutron diffraction data. With XAS and XES at the O K-edge in comparison with band structure calculations of the unoccupied oxygen states, the band gaps of REScO3 were determined and it was found that these values are corresponding to the Sc-O mean distances. The electronic and magnetic structure of LuFe2O4 was presented. The valence state of Fe ions was determined to 50% divalent and 50% trivalent by XPS of Fe 2p and 3s levels. The big orbital magnetic moment found by XMCD could explain a discrepancy between the magnetic measurements and the spin configuration, which was confirmed by XMCD.
Schlagworte: XPS; XMCD; XAS; XES; rare earth scandates; LSMO; LuFe2O4
Erscheinungsdatum: 8-Jun-2009
Enthalten in den Sammlungen:FB04 - E-Dissertationen

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