Abstract

Soft x-ray resonant powder diffraction has been performed at the Mn L2,3 edges of A-site-ordered SmBaMn2O6. The energy and polarization dependences of the (1/4 1/4 0) reflection provide direct evidence for a (x2−z2)/(y2−z2)-type orbital ordering in contrast to single-layer manganite. The temperature dependence of the reflection indicates an orbital reorientation transition at [approximate]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.