Screening and retardation effects on180°-domain wall motion in ferroelectrics: Wall velocity and nonlinear dynamics due to polarization-screening charge interactions

Abstract

The effect of the domain wall intrinsic width, relaxation time of the screening charges, and the dead layer thickness on the velocity of the planar $180\ifmmode^\circ\else\textdegree\fi{}$-domain wall moving under homogeneous external electric field in ferroelectric capacitor is analyzed. The limiting cases of domain wall motion, including (i) the motion induced by the external and local internal field originated at the wall-surface junction for nonzero dead layer thickness and (ii) the motion induced by the effective electric field averaged over the domain wall surface, are considered. We demonstrate the crossover between two screening regimes: the first one corresponds to the low domain wall velocity, when the wall drags the sluggish screening charges, while the second regime appears for high domain wall velocity, when the delay of sluggish screening charges are essential and the wall depolarization field is screened by the instant free charges located at the electrode. The integral and approximate analytical expressions for electric field and algebraic equation for the domain wall velocity are derived. It is shown that in the local-field limit the motion can be unstable, since the internal field at the wall-surface junction decreases for larger domain wall velocities, making possible self-acceleration of the wall near the top surface. The instability may lead to the domain wall-surface bending and actual broadening in thick samples, as well as formation of periodic domain structures in the direction of wall motion. The motion in the limit of the averaged effective field is always stable.