Absence of dipole glass transition for randomly dilute classical Ising dipoles

Dilute dipolar systems in three dimensions are expected to undergo a spin glass transition as the temperature decreases. Contrary to this, we find from Wang-Landau Monte Carlo simulations that at low concentrations x, dipoles randomly placed on a cubic lattice with dipolar interactions do not undergo a phase transition. We find that in the thermodynamic limit the "glass" transition temperature T-g goes to zero as 1/root N, where N is the number of dipoles. The entropy per particle at low temperatures is larger for lower concentrations (x=4.5%) than for higher concentrations (x=20%).