The checkerboard pattern of Bi0.63Sr0.37MnO3 determined using resonant x-ray scattering at the Mn K edge

Abstract

A study using resonant x-ray scattering at the Mn K edge has been carried out on aBi0.63Sr0.37MnO3 single crystal. This compound undergoes a metal–insulator phase transition to theso-called charge ordered (CO) state at about 530 K. Strong resonance signalswere observed at room temperature as the energy was tuned through the MnK edge for several superstructures of the CO phase. The energy, polarizationand azimuth angle dependences agree with a checkerboard ordering in theab plane of manganese atoms of two types, in terms of their different local geometricalstructures. One of the sites is anisotropic—a tetragonal distorted oxygenoctahedron—and the other is isotropic—a nearly undistorted one, as observed forBi0.5Sr0.5MnO3 and other half-doped manganites. This result indicates that thecheckerboard pattern is strongly stable and extends to doping concentrationsx<0.5. No superstructures corresponding to the doubling of thec axis were detected. Intermediate valence states lower than 3.5, according to thefractional charge segregation, were deduced for the two non-equivalent Mn atoms,i.e. Mn3.30+ and Mn3.44+.