THERMODYNAMICS OF 2-DIMENSIONAL XXZ EASY-PLANE QUANTUM HEISENBERG MAGNETS

We consider the quantum easy-plane (XXZ) magnet on the square lattice. In the classical case the system exhibits the Berezinskii-Kosterlitz- Thouless transition. Simulations, both for ferro- and antiferromagnets , using the method of the effective classical Hamiltonian, are made fo r different spin values and refer to the specific heat, the static spi n correlation functions and correlation lengths in a broad range of te mperatures, below and above the transition. The effects of quantum flu ctuations are quantitatively evaluated and discussed. (C) 1997 America n Institute of Physics.