1/N expansion for two-dimensional quantum ferromagnets

The magnetization of a two-dimensional ferromagnetic Heisenberg model, which represents a quantum Hall system at filling factor ν=1, is calculated employing a large N Schwinger boson approach. Corrections of order 1/N to the mean-field (N=∞) results for both the SU(N) and the O(N) generalization of the bosonized model are presented. The calculations are discussed in detail and the results are compared with quantum Monte Carlo simulations as well as with recent experiments. The SU(N) model describes both Monte Carlo and experimental data well at low temperatures, whereas the O(N) model is much better at moderate and high temperatures.