  Ultrathin magnetic films can be modeled as an anisotropic Heisenberg model
with long range dipolar interactions. It is believed that the phase diagram
presents three phases: A ordered ferromagnetic phase (I), a phase characterized
by a change from out-of-plane to in-plane in the magnetization (II), and a high
temperature paramagnetic phase (III). It is claimed that the border lines from
phase I to III and II to III are of second order and from I to II is first
order. In the present work we have performed a very careful Monte Carlo
simulation of the model. Our results strongly support that the line separating
phase II and III is of the BKT type.
