Magnetic phase diagrams of the antiferromagnetic planar model on a stacked triangular lattice

The classical antiferromagnetic planar (XY) model on a simple hexagonal lattice with an applied in-plane magnetic field is studied. With only nearest-neighbor exchange interactions along the c axis, J_∥==1, and in the basal plane, J_⊥, the ground-state (T=0) phase diagram (H,J_⊥) exhibits an unexpected richness of ordered states. Finite-temperature effects treated within a molecular-field approximation for a number of values of J_⊥ reveal complicated (H,T) phase diagrams. Detailed Monte Carlo simulation results are presented for the case of J_⊥=1 and compared with recent predictions associated with chiral multicritical behavior.