Magnetic order in BaMn2As2 from neutron diffraction measurements

Neutron diffraction measurements have been performed on a powder sample of BaMn2As2 over the temperature T range from 10 to 675 K. These measurements demonstrate that this compound exhibits collinear antiferromagnetic ordering below the Neel temperature T-N=625(1) K. The ordered moment mu = 3.88(4)mu(B)/Mn at T = 10 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 Mn2+ 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 AFe(2)As(2) (A = Ca, Sr, Ba, and Eu) compounds, no structural distortion is observed in the magnetically ordered state of BaMn2As2. Our results indicate that while next-nearest-neighbor interactions are important in the AFe(2)As(2) materials, nearest-neighbor interactions are dominant in BaMn2As2.