New Stacking Variations of the Charge and Orbital Ordering in the Metal-Ordered Manganite YBaMn₂O₆

Abstract

We performed transmission electron microscopy (TEM) and powder neutron diffraction experiments on an A-site ordered manganese perovskite YBaMn₂O₆ which undergoes unusual and multiple phase transitions. In the paramagnetic insulating phase, the so-called CE type of charge and orbital ordering was observed in the monoclinic a–b plane, which has been frequently observed for the ordinary solid solution of A_1−x³⁺A_x^′2+MnO₃ around x=0.5. TEM revealed, however, a fourfold periodicity along the c axis, suggesting a new stacking pattern, in which planes of the CE type are built up according to the sequence [ααββ…]. Interestingly, when the system entered the antiferromagnetic state below 195 K, this stacking pattern changed into [αααα…] or [αβαβ…], suggesting a close interplay between spins and orbitals. The obtained stacking patterns were strongly correlated to the inherent structural alternation, i.e., the Y/Ba order along the c axis.