  The properties of spin polarized neutron matter are studied both at zero and
finite temperature using Skyrme-type interactions. It is shown that the
critical density at which ferromagnetism takes place decreases with
temperature. This unexpected behaviour is associated to an anomalous behaviour
of the entropy which becomes larger for the polarized phase than for the
unpolarized one above a certain critical density. This fact is a consequence of
the dependence of the entropy on the effective mass of the neutrons with
different third spin component and a new constraint on the parameters of the
effective Skyrme force is derived in order to avoid such a behaviour.
