1 N EXPANSION FOR 2-DIMENSIONAL QUANTUM FERROMAGNETS/

The magnetization of a two-dimensional ferromagnetic Heisenbrg model, which represents a quantum Hall system at filling factor nu=1, is calc ulated employing a large N Schwinger boson approach. Corrections of or der 1/N to the mean-field (N=infinity) results for both the SU(N) and the O(N) generalization of the bosonized model are presented. The calc ulations are discussed in derail and the results are compared with qua ntum Monte Carlo simulations as well as with recent experiments. The S U(N) model describes both Monte Carlo and experimental data well at lo w temperatures, whereas the O(N) model is much better at moderate and high temperatures. [S0163-1829(98)00727-9].