Magnetic structure of a frustrated honeycomb-lattice antiferromagnet, CaMn2As2.

We wish to perform neutron powder diffraction measurements on triturated crystals of a frustrated honeycomb-lattice antiferromagnet, CaMn2As2, at temperatures below and above its magnetic phase transition at TN = 62 K. We expect to collect data suitable for solving the low-T magnetic structure of CaMn2As2 and also for exploring its magnetic behavior above TN. Our interest in this material was simulated by reports indicating that an isostructural and isoelectronic compound, CaMn2Sb2, is located close to a tricritical point known for the J1-J2-J3 classical Heisenberg model of spins on a honeycomb lattice. Near this point, the Néel phase and two different spiral phases become degenerate and therefore strong magnetic frustration is expected. While CaMn2Sb2 adopts the Néel phase, for CaMn2As2 an incommensurate spiral magnetic structure is suspected based on the recently reported 75As nuclear magnetic resonance study. The accurate determination of the low-temperature magnetic ordering in CaMn2As2 is the primary goal of the proposed experiment. The expected results will be used to locate this compound on the Heisenberg phase diagram, they will inform theoretical studies and guide our doping attempts aiming at inducing a spin liquid state.