Collinear antiferromagnetism in trigonal SrMn$_{2}$As$_{2}$ revealed by single crystal neutron diffraction

FeAs-based compounds and related materials have been an area of intense research in understanding the complex interplay between magnetism and superconductivity. Here we report on the magnetic structure of SrMn$_{2}$As$_{2}$ that crystallizes in a trigonal structure (P$\bar{3}$m1) and undergoes an antiferromagnetic (AFM) transition at $T_N$ $\approx$ 120 K. The temperature dependence of the magnetic susceptibility remains nearly constant below $T_N$ with $H\parallel c$ while it decreases significantly with $H\parallel ab$. This shows that the local Mn moments order and lie in the $ab$ plane instead of aligning along the $c$ axis as in BaMn$_{2}$As$_{2}$. Single crystal neutron diffraction measurements on SrMn$_{2}$As$_{2}$ determined that the Mn moments are collinearly aligned in a G-type AFM order with AFM alignments between a moment and all nearest neighbors in the basal plane and also perpendicular to it. This manifests that G-type AFM order is robust for Mn122 systems despite different symmetries, i.e. tetragonal for BaMn$_{2}$As$_{2}$ and trigonal for SrMn$_{2}$As$_{2}$.\\ Work at Ames Laboratory was supported by the DOE, BES, Division of Materials Sciences \& Engineering, through DE-AC02-07CH11358. This research used resources at University of Missouri Research Reactor.