Resonant soft x-ray powder diffraction study to determine the orbital ordering in a-site-ordered SmBaMn2O6

Abstract

Soft x-ray resonant powder diffraction has been performed at the Mn L-2,L-3 edges of A-site-ordered SmBaMn2O6. The energy and polarization dependences of the (1/4 1/4 0) reflection provide direct evidence for a (x(2) - z(2))/(y(2) - z(2))-type orbital ordering in contrast to single-layer manganite. The temperature dependence of the reflection indicates an orbital reorientation transition at approximate to 210 K, below which the charge- and orbital-ordered MnO2 sheets show AAAA-type of stacking. The concurring reduction of the ferromagnetic superexchange correlations leads to further charge localization. © 2008, American Physical Society