  We present the complete zero temperature phase diagram of a model for
ultrathin films with perpendicular anisotropy. The whole parameter space of
relevant coupling constants is studied in first order anisotropy approximation.
Because the ground state is known to be formed by perpendicular stripes
separated by Bloch walls, a standard variational approach is used, complemented
with specially designed Monte Carlo simulations. We can distinguish four
regimes according to the different nature of striped domains: a high anisotropy
Ising regime with sharp domain walls, a saturated stripe regime with thicker
walls inside which an in-plane component of the magnetization develops, a
narrow canted-like regime, characterized by a sinusoidal variation of both the
in-plane and the out of plane magnetization components, which upon further
decrease of the anisotropy leads to an in-plane ferromagnetic state via a spin
reorientation transition (SRT). The nature of domains and walls are described
in some detail together with the variation of domain width with anisotropy, for
any value of exchange and dipolar interactions. Our results, although strictly
valid at $T=0$, can be valuable for interpreting data on the evolution of
domain width at finite temperature, a still largely open problem.
