Microscopic model of domain wall motion

Abstract

Polarization switching is simulated using a model based on a sequence of single dipole flips. The single dipole flips are assumed to be thermally activated with transition rates depending on the local field. The time to switch a single dipole depends on the deterministic transition rate and on a probabilistic factor. In each step, the dipole with the shortest flip time is switched. We investigate one dimensional dipole chains as well as two and three dimensional systems based on the barium titanate structure that comprises single charges fluctuating in double well potentials and induced dipoles. The two and three dimensional simulations yield intrinsic dead layers close to the electrodes that can not be switched even in very strong fields. These non switchable layers are nuclei for the domain wall motion and thus nuclei for the switching process. The switching time of the system decreases faster than exponential for low fields with increasing field. This decrease slows down for higher fields. Furthermore, we found intrinsic dead layers around a defect.