The checkerboard pattern of Bi(0.63)Sr(0.37)MnO(3) determined using resonant x-ray scattering at the Mn K edge

A study using resonant x-ray scattering at the Mn K edge has been carried out on a Bi(0.63)Sr(0.37)MnO(3) single crystal. This compound undergoes a metal-insulator phase transition to the so-called charge ordered (CO) state at about 530 K. Strong resonance signals were observed at room temperature as the energy was tuned through the Mn K edge for several superstructures of the CO phase. The energy, polarization and azimuth angle dependences agree with a checkerboard ordering in the ab plane of manganese atoms of two types, in terms of their different local geometrical structures. One of the sites is anisotropic-a tetragonal distorted oxygen octahedron-and the other is isotropic-a nearly undistorted one, as observed for Bi(0.5)Sr(0.5)MnO(3) and other half-doped manganites. This result indicates that the checkerboard pattern is strongly stable and extends to doping concentrations x<0.5. No superstructures corresponding to the doubling of the c axis were detected. Intermediate valence states lower than 3.5, according to the fractional charge segregation, were deduced for the two non-equivalent Mn atoms, i.e. Mn(3.30+) and Mn(3.44+).