Abstract
Nature of ordered phases of Ising-like Heisenberg antiferromagnets on the hexagonal (layered triangular) lattice is investigated by making use of a Monte Carlo method and mean field analysis. Two phase transitions are found, which correspond to the orderings of the z-component and of the xy-components of the spins, respectively. The uniform magnetization along the easy axis is found in ordered phases with a concave curve as a function of the temperature and the spin configuration of the ordered phases is found to be a three-sublattice ferrimagnetic one. In the low temperature phase, the effect of the nontrivial degeneracy (NTD) of the ground state which is inherent to the present model is investigated. NTD causes a nontrivial enhancement of the fluctuation of the uniform magnetization in the hard plane. The magnetization processes in the ground state for fields along the x-axis are also studied.
