  By tempered Monte Carlo simulations, an Almeida-Thouless (AT) phase-boundary
line in site-diluted Ising spin systems is searched for. Spins interact only
through dipolar fields and occupy a small fraction of lattice sites. The
spin-glass susceptibility of these systems and of the Sherrington-Kirkpatrick
model are compared. The correlation length as a function of system size and
temperature is also studied. The results obtained are contrary to the existence
of an AT line.
