Memory effects and slow dynamics in ultra thin magnetic films

Monte Carlo studies of a uniaxial spin system on a square lattice with both ferromagnetic exchange interactions and dipolar interactions reveal three distinct dynamical regimes at low temperatures. In the first regime the magnetization decays through nucleation and growth of spin islands, in the second regime, despite the magnetization being effectively zero, there is a persistent memory effect most clearly revealed by the asymmetry between the numbers of up and down islands. The third regime is characterized by slow crystallization of the equilibrium smectic phase from the quenched polycrystalline state.