We report the characterization of the layered rare-earth manganese oxyselenide ${\text{La}}_2{\text{O}}_3{\text{Mn}}_2{\text{Se}}_2$. The susceptibility data show a broad maximum near 350 K, indicating the existence of two-dimensional (2D) short-range ordering in this compound. A sharp feature associated with a short-range to long-range antiferromagnetic phase transition is seen at 163 K. A very small heat-capacity anomaly is detected around 163 K, indicating that most of the magnetic entropy is lost during the 2D ordering process. Both crystal and magnetic structures were studied by neutron powder diffraction at 300, 200, 150, 100, and 6 K. The structure was refined in space group $I4/mmm$ with $a=4.13939\left(3\right)\text{Å}$ and $c=18.8511\left(2\right)\text{Å}$ at ambient temperature. No structural distortion was detected. The resulted magnetic structure is G-type with a propagation vector of $\mathbf{k}=\left(0,0,0\right)$ and an ordered magnetic moment of $4.147\left(28\right){\mu }_B/\text{Mn}$ along $c$ is found at 6 K. Warren peak shape analysis of the neutron-diffraction data near $22°$ is employed to characterize the increase in correlation length in the 2D magnetic state on approaching the three-dimensional ordering transition.

• Received 29 September 2010

DOI:https://doi.org/10.1103/PhysRevB.82.214419