Size effects in ferroelectric thin films:: 180° domains and polarization relaxation

The role of 180 degrees domain kinetics on size effects in ferroelectric thin films is studied within a time-dependent Ginzburg-Landau framework. The model incorporates the effect of the depolarization field by considering nonferroelectric-passive layers at the top and bottom surfaces. A critical length scale is predicted below which a depolarization field-induced spontaneous transition from a single domain to a 180 degrees domain pattern causes a time-dependent relaxation of the remnant polarization. This is consistent with the experiments by Kim [Phys. Rev. Lett. 95, 237602 (2005)], where a frequency dependence of the remnant polarization has indeed been observed.