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Co Physisorbed On Ionic Crystals: An Extended Beg Spin-Lattice Model Of Absorbed Dipolar Molecules, T. E. Burns, John R. Dennison

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The 2D dielectric phases and phase transitions of adsorbed dipolar molecules are studied using a dilute spin-one Ising model. The spin-one formulation assigns a spin S_i=±1 to a (up/down) dipole occupying a lattice site I adsorbed perpendicular to the substrate surface and S_i=0 to unoccupied sites. We relate the mean field expression for the spin-model interaction energy to a more detailed microscopic model involving dipolar, quadrupolar and repulsive interactions beyond nearest neighbor. Analytic solutions in the mean field approximation are discussed for dipole-orientation order–disorder transitions and ferroelectric-to-antiferroelectric transitions as a function of temperature and coverage. The …