Manipulation of charged domain walls in geometric improper ferroelectric thin films: A phase-field study

Abstract

Using phase-field simulations, we show how interfaces acting on the geometric-improper ferroelectric polarization of hexagonal manganite and ferrite thin films can be used to control the formation of charged domain walls. We modify the Landau expansion of the free energy valid in bulk to emulate interface effects known from previous cross-sectional experiments, and we verify our model by comparing our results with images obtained in these experiments. We then show how the interface affects the orientation of ferroelectric domain walls in the fully three-dimensional case. Furthermore, we demonstrate that interface effects combined with an external electric field enable us to specifically choose the dominant domain-wall type (head-to-head, tail-to-tail, or neutral). We also find that an electric field can stabilize a novel domain-wall type which only emerges in the improper ferroelectric order but not in the primary structural distortion. Since the domain walls have a conductivity that is different from the interior of the domains, the influence of the interfaces of a thin film on the type and distribution of the walls gives us the possibility to control the transport properties of a material by appropriate thin-film engineering.