Magnetic Phase Diagram for the Triangular Ising Lattice with Antiferromagnetic Nearest-Neighbor and Ferromagnetic Next-Nearest-Neighbor Interactions

Abstract

The cluster variation method is applied to calculate a temperature versus magnetic field phase diagram for the triangular Ising lattice with antiferromagnetic nearest-neighbor (nn) and ferromagnetic next-nearest-neighbor (nnn) interactions. Calculations are performed within the nn equilateral triangle plus nnn equilateral triangle approximation as well as within the molecular field approximation. The phase diagrams obtained within the former approximation are in good agreement with the Monte Carlo results of other authors except in the region of small magnetic field. The temperature and magnetic field dependence of sublattice magnetizations, total magnetization, specific heat, and susceptibility is calculated. A brief discussion is given in connection with experimental data on CsCoCl₃ and CsCoBr₃.