Neutron diffraction measurements have been performed on a powder sample of ${\text{BaMn}}_2{\text{As}}_2$ over the temperature $T$ range from 10 to 675 K. These measurements demonstrate that this compound exhibits collinear antiferromagnetic ordering below the Néel temperature $T_{\text{N}}=625\left(1\right)\text{K}$. The ordered moment $\mu =3.88\left(4\right){\mu }_{\text{B}}/\text{Mn}$ at $T=10\text{K}$ is oriented along the $c$ axis and the magnetic structure is $G$ type, with all nearest-neighbor Mn moments antiferromagnetically aligned. The value of the ordered moment indicates that the oxidation state of Mn is ${\text{Mn}}^{2+}$ with a high spin $S=5/2$. The $T$ dependence of $\mu$ suggests that the magnetic transition is second order in nature. In contrast to the closely related $A{\text{Fe}}_2{\text{As}}_2$ ($A=\text{Ca}$, Sr, Ba, and Eu) compounds, no structural distortion is observed in the magnetically ordered state of ${\text{BaMn}}_2{\text{As}}_2$. Our results indicate that while next-nearest-neighbor interactions are important in the $A{\text{Fe}}_2{\text{As}}_2$ materials, nearest-neighbor interactions are dominant in ${\text{BaMn}}_2{\text{As}}_2$.

• Received 22 July 2009

DOI:https://doi.org/10.1103/PhysRevB.80.100403