We report neutron-diffraction results on single-crystal CaMn2P2
containing corrugated Mn honeycomb layers and determine its ground-state
magnetic structure. The diffraction patterns consist of prominent (1/6, 1/6,
L) reciprocal lattice unit (r.l.u.; L = integer) magnetic Bragg
reflections, whose temperature-dependent intensities are consistent with a
first-order antiferromagnetic phase transition at the N\'eel temperature
TN=70(1) K. Our analysis of the diffraction patterns reveals an
in-plane 6×6 magnetic unit cell with ordered spins that in the
principal-axis directions rotate by 60-degree steps between nearest neighbors
on each sublattice that forms the honeycomb structure, consistent with the
PAc magnetic space group. We find that a few other magnetic subgroup
symmetries (PA2/c, PC2/m, PS1ˉ,PC2,PCm,PS1) of the
paramagnetic P3ˉm11′ crystal symmetry are consistent with the
observed diffraction pattern. We relate our findings to frustrated
J1-J2-J3 Heisenberg honeycomb antiferromagnets with single-ion
anisotropy and the emergence of Potts nematicit