Abstract
Resonant x-ray scattering (RXS) at the Mn edge has been used to characterize the low temperature ordered phase of . Strong resonances were observed for the (030), (050), , , , and reflections as the photon energy is tuned through the Mn edge. The reported azimuthal and polarization dependence of the resonant intensities indicates that the low temperature phase is described as a checkerboard ordering of two types of Mn sites with different local geometrical structures. One of the sites is anisotropic, a tetragonal distorted oxygen octahedron and the other one is isotropic, a nearly undistorted oxygen octahedron. The distinction of these two Mn sites is accompanied by a displacement of the Mn atoms transverse to the axis. We conclude that this checkerboard-ordered pattern is a common ground state in half-doped manganites. Intermediate valence states according to fractional charge segregation were deduced for the two nonequivalent Mn atoms, far from the localized and ionic species. Hence, the experimental data discard the ionic model of charge and orbital ordering of localized (or -like) states at the Mn site (or the cluster). We suggest a description of the RXS in terms of band structure effects and lattice dynamics.
5 More- Received 31 May 2005
DOI:https://doi.org/10.1103/PhysRevB.73.205107
©2006 American Physical Society