  We introduce a lattice spin model that mimics a system of interacting
particle through a short range repulsive potential and a long range attractive
power law decaying potential. We performed a detailed analysis of the general
equilibrium phase diagram of the model at finite temperature, showing that the
only possible equilibrium pases are the ferromagnetic and the antiferromagnetic
ones. We then studied the non equilibrium behavior of the model after a quench
to subcritical temperatures, in the antiferromagnetic region of the phase
diagram region, where the pair interaction potential behaves in the same
qualitative way as in a Lennard-Jones gas. We found that, even in the absence
of quenched disorder or geometric frustration, the competition between
interactions gives rise to non--equilibrium disordered structures at low enough
temperatures that strongly slow down the relaxation of the system.
