Magnetic order in the polar intermetallic CaMn2Sb2 studied via powder neutron diffraction.

This paper reports a neutron powder diffraction study of CaMn2Sb2 in the temperature range of 20-300 K. Short-range magnetic order, characterized by a broad diffraction peak corresponding to a d spacing of 4 , is observed between 120 and 200 K. Collinear long-range antiferromagnetic order of manganese ions occurs below 85 K, where a transition is observed in the DC magnetic susceptibility measured on a single crystal. The long range antiferromagnetic order is characterized by a propagation vector k = (0 0 0) with a magnetic moment of 3.38 μB at 20 K. Two possible magnetic models have been identified, which differ in the orientation of the spins with respect to the ab plane. The model with the spins oriented at a 25(2)o angle relative to the ab plane gives an improved fit compared to the other model in which the spins are constrained to the ab plane. Representational analysis cannot account for a model involving a c-axis component without the mixing of two irreducible representations, suggesting the presence of first-order character in the phase transition.