Magnetic order in BaMn2 As2 from neutron diffraction measurements

Neutron diffraction measurements have been performed on a powder sample of BaMn2 As2 over the temperature T range from 10 to 675 K. These measurements demonstrate that this compound exhibits collinear antiferromagnetic ordering below the Néel temperature TN =625 (1) K. The ordered moment μ=3.88 (4) μB /Mn at T=10K 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 Mn2+ with a high spin S=5/2. The T dependence of μ suggests that the magnetic transition is second order in nature. In contrast to the closely related A Fe2 As2 (A=Ca, Sr, Ba, and Eu) compounds, no structural distortion is observed in the magnetically ordered state of BaMn2 As2. Our results indicate that while next-nearest-neighbor interactions are important in the A Fe2 As2 materials, nearest-neighbor interactions are dominant in BaMn2 As2. © 2009 The American Physical Society.