We will study successive phase transitions in the magnetization process of weakly XY-like Heisenberg S=1/2 Antiferromagnets on the triangular lattice. The classical version of this model exhibits a complicated series of phases in the magnetization process at finite temperature, which are induced by thermal effects, i.e., the entropy effect. The similar successive phase transitions are found in the ground state of the S=1/2 system, which is induced by the quantum fluctuation. We will also refer properties on so-called triangle-tube models.

Department of Physics, University of Tokyo, Japan