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

Abstract

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, ${\mathit{J}}_{\mathrm{\parallel }}$==1, and in the basal plane, ${\mathit{J}}_{\mathrm{\perp }}$, the ground-state (T=0) phase diagram (H,${\mathit{J}}_{\mathrm{\perp }}$) exhibits an unexpected richness of ordered states. Finite-temperature effects treated within a molecular-field approximation for a number of values of ${\mathit{J}}_{\mathrm{\perp }}$ reveal complicated (H,T) phase diagrams. Detailed Monte Carlo simulation results are presented for the case of ${\mathit{J}}_{\mathrm{\perp }}$=1 and compared with recent predictions associated with chiral multicritical behavior.