Regensburg 2004 – wissenschaftliches Programm
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TT: Tiefe Temperaturen
TT 14: FV-internes Symposium ”Orbital Physics”
TT 14.5: Vortrag
Dienstag, 9. März 2004, 15:50–16:05, H18
Orbital degree of freedom in manganites determined by O1s and Mn2p NEXAFS: crystal field versus orbital coupling in single-layered La1−xSr1+xMnO4 — •Michael Merz1, P. Reutler2, B. Büchner2, Y. U. Idzerda3, S. Tokumitsu4, N. Nücker4, and S. Schuppler4 — 1Institut für Kristallographie, RWTH Aachen — 2Institut für Festkörper- und Werkstoffforschung, Dresden — 3Naval Research Laboratory, Washington — 4Forschungszentrum Karlsruhe, Institut für Festkörperphysik
Manganites exhibit a manifold of highly interesting magnetic and electronic phases, with charge- and orbital-ordered states being at the center of interest. Especially single-layered La1−xSr1+xMnO4 is a prototypical example for such ordering effects. For this compound a ferro-orbital ordering of |3z2−r2> states is expected from the strong crystal field, yet anti-ferro type orbital coupling might lead to an admixture of |x2−y2> states.
Using polarization-dependent O1s and Mn2p near-edge x-ray absorption spectroscopy on untwinned La1−xSr1+xMnO4 single crystals (0 ≤ x ≤ 0.5), the doping- and temperature-dependent occupancies of the O2p and Mn3d orbitals were studied. According to the spectra, Sr doping not only provides holes to the system but also induces a continuous transfer of electrons from out-of-plane |3z2−r2> to in-plane |3x2−r2> and |3y2−r2> states. The data clearly demonstrate that electrons reside for all doping levels on mixed α |3z2−r2> + β |x2−y2> states, i. e., antiferro-coupled canted orbitals where α and β strongly depend on the Sr content.