Polarization-dependent resonant-x-ray diffraction in charge- and orbital-ordering phase of Nd_1/2Sr_1/2MnO₃

A study of resonant-x-ray scattering in a charge-ordered perovskite manganese oxide Nd_1/2Sr_1/2MnO₃ was performed. Dipole-resonant superlattice reflections originating from the orderings of the charge and orbital with Q_charge = (0,1,0) and Q_orbital = (0,1/2,0) in the Pbnmsetting were observed. Sudden change in the intensity of the superlattice scattering at the transition temperature indicated a strong first-order phase transition. Characteristic dependence on the x-ray polarization was observed not only for orbital-order superlattice scattering but also for charge-order scattering. It should be closely related to the orbital-ordering type (d_3x²-r²/d_3y²-r²)or (d_x²-z²/d_y²-z²).