  The phase diagram of the classical anisotropic (XXZ) Heisenberg model on the
2-dimensional triangular lattice is investigated using Monte Carlo methods. In
the easy-axis limit, two finite temperature vortex unbinding transitions have
been observed. In the easy-plane limit, there also appear to be two distinct
finite temperature phase transitions. The upper transition corresponds to an
Ising-like chirality ordering and the lower temperature transition corresponds
to a Kosterlitz-Thouless vortex unbinding transition. These phase transition
lines all meet at the Heisenberg point and provide strong evidence that the
isotropic model undergoes a novel finite temperature phase transition.
