Charge, orbital and magnetic ordering in La0.4Sr1.6MnO4

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. 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. 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.