  We analyze the nature of the phase transition from a smectic stripe phase to
a tetragonal phase predicted in analytic studies by Abanov et al. (Phys. Rev. B
51, 1023 (1995)) and observed in experiments on ultra-thin magnetic films by
Vaterlaus et al.(Phys. Rev. Lett. 84, 2247 (2000)). At variance with existent
numerical evidence, for the first time we show results of Monte Carlo
simulations on a two-dimensional model with competing exchange and dipolar
interactions showing strong evidence that the transition is a weak first order
one, in agreement with the theoretical predictions of Abanov et al. Besides the
numerical evidence, we give further support to the first order nature of the
transition analyzing a continuum version of the model and showing that it
belongs to a large family of systems, or universality class, in which a first
order transition driven by fluctuations is expected on quite general grounds.
