Frustrated magnetic cycloidal structure and emergent Potts nematicity in CaMn2P2

We report neutron-diffraction results on single-crystal ${\mathrm{CaMn}}₂{\mathrm{P}}₂$ containing corrugated Mn honeycomb layers, and we 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 ${T}_{\mathrm{N}}=70(1)$ K. Our analysis of the diffraction patterns reveals an in-plane $6\ifmmode\times\else\texttimes\fi{}6$ magnetic unit cell with ordered spins that in the principal-axis directions rotate by ${60}^{\ensuremath{\circ}}$ steps between nearest neighbors on each sublattice that forms the honeycomb structure, consistent with the ${P}_Ac$ magnetic space group. We find that a few other magnetic subgroup symmetries (${P}_A2/c$, ${P}_C2/m$, ${P}_S\overline{1},{P}_C2,{P}_Cm,{P}_S1$) of the paramagnetic $P\overline{3}m{11}^{\ensuremath{'}}$ crystal symmetry are consistent with the observed diffraction pattern. We relate our findings to frustrated ${J}₁\text{\ensuremath{-}}{J}₂\text{\ensuremath{-}}{J}₃$ Heisenberg honeycomb antiferromagnets with single-ion anisotropy and the emergence of Potts nematicity.