Phase transitions and magnetic structures in the antiferromagnetic Potts model

The antiferromagnetic 3-state Potts model on a body-centered cubic lattice with competing interactions of the first ($J_{1}$) and second ($J_{2}$) nearest-neighbor was studied by the Monte Carlo method. A phase diagram of the critical temperature dependence on the value $J_{2}$ was constructed. The competition of exchange interactions in the range $-2/3<J_{2}<0$ was determined to result in a phase separation and a change in the phase transition order. In the low-temperature region, an ordered phase, lying inside a partially disordered phase with broken sublattice symmetry, was found. In addition, at $J_{2}\leqslant -2/3$, a phase with broken sublattice symmetry state of a different type arises. The magnetic structures of the ground state corresponding to different regions of the phase diagram were established.