We report a single-crystal neutron diffraction study of the crystal and magnetic structures of ${\mathrm{NdBaMn}}_2{\mathrm{O}}_6$ 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 ${\mathrm{NdBaMn}}_2{\mathrm{O}}_6$. We find that both the paramagnetic and antiferromagnetic insulating phases adopt a $2\sqrt{2}{a}_p\times \sqrt{2}{a}_p\times 2c_p$ unit cell with space group $P{2}_{1}am$ and exhibit $(3x^2-r^2)/(3y^2-r^2)$-type charge and orbital ordering. 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.

Close

PrevNext

View figure in article

• Antiferromagnetism
• Charge order
• Colossal magnetoresistance
• Electrical conductivity
• Ferroelectricity
• Magnetic order
• Magnetic phase transitions
• Magnetic susceptibility
• Orbital order
• Strongly correlated systems