Quantum Monte Carlo study of low dimensional magnetic system

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.