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The ground state configuration of generalized Heisenberg models, H = - Σ≪ij>Jxy(SixSjx + SiySjy) + JzSizSjz; - ∞ ≪ Jxy, Jz ≪ ∞, on the triangular lattice is investigated. Their thermodynamic properties are also studied by a harmonic approximation and by Monte Carlo simulation. In particular, reentrant phase transitions are found for the case Jz > 0 and Jz/Jxy > -0.5. Successive phase transitions are also found for the case Jz ≪ 0 and −0.5 ≪ Jxy/Jz ≪ 1.0. Including the pure ferromagnetic case, a general phase diagram is presented.
Seiji Miyashita (Wed,) studied this question.