Regensburg 2004 – wissenschaftliches Programm

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TT: Tiefe Temperaturen

TT 24: Postersitzung III: Korrelierte Elektronen, ”Orbital Physics”

TT 24.2: Poster

Mittwoch, 10. März 2004, 14:30–19:00, Poster A

Charge and orbital order in Fe₃O₄ — •I. Leonov^1,2, A. N Yaresko³, V. N. Antonov⁴, M. A. Korotin², V. I. Anisimov², and D. Vollhardt¹ — ¹Theoretical Physics III, University of Augsburg, 86135 Augsburg — ²Institute of Metal Physics, Ekaterinburg GSP-170, Russia — ³Max Planck Institute for Physics of Complex Systems, 01187 Dresden — ⁴Institute of Metal Physics, 03142 Kiev, Ukraine

The issue of charge and orbital ordering in the low-temperature monoclinic (P2/c) structure of magnetite (Fe₃O₄)[1] is investigated using LSDA+U. The ground state is found to display both charge order (CO) and orbital order (OO) [2]. The CO is described by a [001] charge density wave with a minor [001/2] modulation, and is incompatible with the Anderson criterion. The OO agrees with the Kugel-Khomskii theory. The system is described by two order parameters: (i) the difference between the t_2g minority occupancies of 2+ and 3+ Fe cations, and (ii) the total 3d charge difference. While the former is large (0.5), the screening of charge disproportion is so effective that the latter is rather small (0.23). This agrees well with the results of bond valence sum analysis (0.2). The LSDA+U results are also in reasonably good with measured optical spectra.

[1] J. P. Wright, J. P. Attfield and P. G. Radaelli, Phys. Rev. Let. 87, 266401 (2001)

[2] I. Leonov, A. N. Yaresko, V. N. Antonov, M. A. Korotin, V. I. Anisimov and D. Vollhardt (preprint)