Monte Carlo study of a two-dimensional quantum ferromagnet

We present quantum Monte Carlo results for the field and temperature depend ence of the magnetization and the spin lattice relaxation rate 1/T-1 of a t wo-dimensional S = 1/2 quantum Heisenberg ferromagnet. The Monte Carlo meth od, which yields results free of systematic errors, is described in detail. The high accuracy of the calculated magnetization allows for stringent tes ts of recent approximate analytical calculations. We also compare our resul ts with recent experimental data for a nu = 1 quantum Hall ferromagnet, whi ch is expected to be well described by the Heisenberg model. The dynamic re sponse function needed to extract 1/T-1 is obtained using maximum-entropy a nalytic continuation of the corresponding imaginary-time dependent correlat ion function. We discuss the reliability of this approach.