  Monte Carlo simulations are performed for the S = 1/2 XY and ferro- and
antiferromagnetic Heisenberg model in two dimensions using the loop algorithm.
Thermodynamic properties of all these models are investigated in wide
temperature range. The energy, specific heat, susceptibility and other
parameters are given as function of temperature and the Trotter number. The
comparison of calculated thermodynamic quantities with theoretical and with
experimental data are given. It is shown that our results are in good agreement
with them.
