Ferroelectiric hysteresis in systems of permanent dipoles: a computer simulation

The electrostatic interaction of bidirectional dipoles and its effect on the polarization has been investigated using a Monte Carlo simulation. Up to 2000 dipoles are located in a space between two parallel electrodes either at cubic lattice sites or at randomly distributed sites. The local fields at each dipole resulting from the external field and the field of all the other dipoles are calculated by the method of images, in an iterative procedure the polarization is calculated and we find that the interaction between randomly distributed dipoles decreases the total polarization. In the system of lattice dipoles the interaction increases the polarization at high temperatures and decreases it at low temperatures. Starting the calculation with identical double wells we find a distribution of activation energies due to the interaction. The lattice and the disordered dipole systems exhibit ferroelectric hysteresis loops of their polarization. The remanent polarization of lattice dipoles drops sharply and for disordered dipoles it drops smoothly with temperature. In both systems we find an increase of the coercive field strength with decreasing distance of the electrodes, i.e. decreasing thickness of the sample.