  The properties of helical thin films have been thoroughly investigated by
classical Monte Carlo simulations. The employed model assumes classical planar
spins in a body-centered tetragonal lattice, where the helical arrangement
along the film growth direction has been modeled by nearest neighbor and
next-nearest neighbor competing interactions, the minimal requirement to get
helical order. We obtain that, while the in-plane transition temperatures
remain essentially unchanged with respect to the bulk ones, the helical/fan
arrangement is stabilized at more and more low temperature when the film
thickness, n, decreases; in the ordered phase, increasing the temperature, a
softening of the helix pitch wave-vector is also observed. Moreover, we show
also that the simulation data around both transition temperatures lead us to
exclude the presence of a first order transition for all analyzed sizes.
Finally, by comparing the results of the present work with those obtained for
other models previously adopted in literature, we can get a deeper insight
about the entwined role played by the number (range) of interlayer interactions
and surface effects in non-collinear thin films.
