Chiral tetracritical behavior in a partially frustrated triangular antiferromagnet: Application toABX3compounds

A Landau-type free energy derived from molecular-field theory serves as the basis for this investigation of the classical XY model on a partially frustrated stacked triangular antiferromagnet composed of two inequivalent magnetic sites. The structure may be viewed as layers of interpenetrating triangular (tripartite) and honeycomb (bipartite) lattices with intralattice (J) and interlattice (J’) exchange coupling. Tetracritical behavior is shown to occur in the temperature-(J’/J) phase diagram, characterized by the convergence of four lines of continuous transitions, where the 120° chiral spin structure is stabilized. Comments are made concerning the possibility to observe such behavior in ${\mathrm{RbFeBr}}_3$ and related compounds through the application of pressure.