Possibility of a Phase Transition for the Two-Dimensional Heisenberg Model

We point out that the existence of a phase transition-as indicated by extrapolation from high-temperature expansions-is as well-founded for two-dimensional lattices with nearest-neighbor ferromagnetic Heisenberg interactions as for three-dimensional lattices, and that the "well-known result" that there exists no phase transition in two dimensions is not a valid conclusion from the standard spin-wave argument.