Single-crystal neutron diffraction study of the insulating phase in NdBaMnO

Yamada, Shigeki*; Kiyanagi, Ryoji  ; Nakao, Akiko*; Sagayama, Hajime*; Arima, Takahisa*

We report a single-crystal neutron diffraction study of the crystal and magnetic structures of NdBaMnO in its insulating phases, performed on a well-characterized sample that exhibits room-temperature low-field colossal magnetoresistance (CMR). Previous studies have reported conflicting results regarding the crystal structure and the presence or absence of charge-orbital ordering, likely due to differences in sample form and measurement techniques. By using a single crystal in which CMR is directly observed, we clarify these inconsistencies and establish a unified structural picture. This study establishes that the insulating phases correspond to a charge- orbital-ordered state in NdBaMnO. We find that the antiferromagnetic phase shows an A-type magnetic structure with inequivalent Mn moments arising from this ordering. These results demonstrate that the insulating phases correspond to a charge- orbital-ordered state and suggest that the observed CMR originates from the competition between charge-orbital ordering and magnetic structures. In addition, the polar crystal symmetry implies the presence of spontaneous polarization, mainly arising from oxygen displacements.