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TT: Tiefe Temperaturen
TT 32: Theoretische Modelierung von Materialien mit korrelierten Elektronen
TT 32.6: Vortrag
Freitag, 12. März 2004, 11:30–11:45, H18
The spin-state puzzle in cobaltates — •Z. Hu1, H. Wu2, D. Madenci1, J. Baier1, T. Lorenz1, I. Bonn3, C. F e lser3, A. Tanaka4, H.H. Hsieh5, H.-J. Lin5, C.T. C h en5, and L.H. Tjeng1 — 1II. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany — 2Max-Plank-Institut für Physik komplexer Systeme, Nöthnitzer Str.38, 01187 Dresden, Germany — 3Johannes Gutenberg-Universität Mainz, Becher Wege 24, 55099 Mainz, Germany 472 — 4Department of Materials Science, Faculty of Science, Hiroshima University, Higaschi-Hiroschima, Japan — 5Synchrotron Radiation Research Center, No. 1 R&D Road VI, Science Based Industrial Park, Hsinchu 300, Taiwan
We have carried out an experimental and theoretical study on the spin-state of the Co3+ ion in the layered Sr2CoO3Cl material. Using soft-x-ray absorption spectroscopy at the Co L2,3 and O K edges, in combination atomic multiplet cluster and LDA+U calculations, we found that the Co3+ ion is in the high spin-state, thereby falsifying all claims reported so far in the literature which were based mostly on neutron, magnetic, or crystallographic measurements. Detailed full-potential LDA+U calculations reveal that the persistent high spin state and insulating behavior of Sr2CoO3Cl are caused by the CoO5 pyramidal coordination and, particularly, by the large plane corrugation of the basal CoO2 layer. Our finding has far reaching implications for other layered cobalt oxides currently under intense debat, e.g., RBaCo2O5+x, the layered double perovskites showing metal-insulator transitions and colossal magneto-resistance.