DIPOLAR SYSTEMS - TRANSITION TO GLASSY ORDERING ON DILUTION

Diluted dipolar Ising systems on a regular lattice are studied numeric ally within the local mean field approximation used for quenched syste ms. We compensate for the demagnetization field by adding a magnetizat ion dependent term to the local field and study different solutions fo r different initial conditions. This added term enables us to distingu ish the glassy stale from the ferromagnetic state which otherwise woul d break up into domains. For high densities of dipoles we obtain a wel l defined ferromagnetic phase, where the solution stays the same, inde pendently of the initial conditions. For diluted systems on the other side, the ferromagnetic phase disappears and is replaced by the glassy state. Different solutions are obtained with almost the same free ene rgy. We find that the concentration x(c), separating these two phases, agrees relatively well with experimental findings. The found transiti on temperatures, however are somewhat higher than the experimental one s for ferromagnetic samples. In the glassy regime this difference incr eases. These deviations are reduced slightly by using the one loop exp ansion, where a reaction term has been subtracted from the effective f ield.