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TT: Fachverband Tiefe Temperaturen

TT 19: CE: Metal-Insulator Transition 2

TT 19.1: Vortrag

Mittwoch, 24. März 2010, 09:30–09:45, H18

Charge, orbital and magnetic ordering in La_0.4Sr_1.6MnO₄ — •Holger Ulbrich¹, Daniel Senff¹, Olaf J. Schumann¹, Yvan Sidis², Paul Steffens³, and Markus Braden¹ — ¹II. 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 La_0.5Sr_1.5MnO₄ can be described by the Goodenough model [1-3]. The over-doped La_0.4Sr_1.6MnO₄ 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).