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TT: Tiefe Temperaturen

TT 20: Metall-Isolator-Überg
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TT 20.4: Vortrag

Mittwoch, 10. März 2004, 15:15–15:30, H18

X-ray magnetic and natural circular dichroism at the vicinity of the Co low-spin to high-spin transition in REBaCo2O5.5 (RE= Dy; Gd) system — •S. Gold1, E. Goering1, P. Lemmens2, A. Podlesnyak3, G. Bychkov4, J. Deisenhofer5, A. Loidl5 und G. Schütz11MPI für Metallforschung, Stuttgart — 2MPI für Festkörperforschung, Stuttgart — 3PSI, ETHZ&PSI, Villingen — 4Inst. of Solid State & Semicond. Phys., Nat. Acad. Sci. Minsk — 5EP5, Universität Augsburg

The magnetic perovskite REBaCo2O5.5 (RE= Dy; Gd) system shows a rich magnetic and electronic phase diagram, with a MI transition at higher temperatures and ferromagnetic ordering just below room temperature. With a further reduction of temperature the ferromagnetic magnetization is strongly reduced. This has been discussed in terms of a Co spin state transition and/or antiferromagnetism. A double peak like structure could be observed in the Co L2,3 XMCD. We interpret this double peak by spectroscopic distinguishable octahedral and pyramidal Co sites. The Co L2,3 XMCD has been separated from the overlapping Ba M4,5 spectra by a recently developed XMCD analysis tool called moment analysis. This analysis exhibits an unusual large orbital/spin-moment ratio. In addition, we could observe an extreme large X-ray natural circular dichroism (XNCD) signal, which is about two orders of magnitude larger compared to other published results and about 20% of the corresponding white line intensity. This suggests a large non centrosymmetric charge distribution at the Co site. Nevertheless, the orgin of this extreme large XNCD effect is not clear up to now.

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DPG-Physik > DPG-Verhandlungen > 2004 > Regensburg