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Regensburg 2010 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 19: CE: Metal-Insulator Transition 2

TT 19.1: Talk

Wednesday, March 24, 2010, 09:30–09:45, H18

Charge, orbital and magnetic ordering in La0.4Sr1.6MnO4 — •Holger Ulbrich1, Daniel Senff1, Olaf J. Schumann1, Yvan Sidis2, Paul Steffens3, and Markus Braden11II. Physikalisches Institut, Universität zu Köln — 2Laboratoire Léon Brillouin, Saclay — 3Institut Laue Langevin, Grenoble

The coupled ordering of charge orbital and spin (COS) degrees of freedom in the manganites constitutes a key element to understand the mechanism of CMR. 214 manganites are well-suited to study the COS state. The COS state of the half-doped layered material La0.5Sr1.5MnO4 can be described by the Goodenough model [1-3]. The over-doped La0.4Sr1.6MnO4 consists of 60% Mn4+ ions and 40% Mn3+ ions. Consequently there is no optimal checkerboard charge ordering possible. We suggest to put these excess of Mn4+ ions into stripes cutting the zig-zag chains. Investigations by neutron scattering emphasize this idea as incommensurable superstructure reflections of charges and orbitals could be found. The reflections of the magnetic ordering of Mn3+ are incommensurable as well, while the magnetic ordering of Mn4+ yields scattering at commensurable positions. These experiments are not in agreement with results by Larochelle et al. [4]. Stripe-like arrangement of Mn4+ ions are similar to the stripe phases in nickelates and cuprates. The order, however, is quite complex involving incommensurate ordering of orbitals, charges and Mn3+-magnetic moments.

[1] D. Senff, et al., Phys. Rev. Lett. 96, 257201 (2006).

[2] D. Senff, et al., Phys. Rev. B 77, 184413 (2008).

[3] J.B. Goodenough, Phys. Rev. 100, 564 (1955).

[4] S. Larochelle et al., Phys. Rev. B 71, 024435 (2005).

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