Deterministic polarization reversal in ferroelectric and multiferroic films is critical for their exploitation in nanoelectronic devices. While ferroelectricity has been studied for nearly a century, major discrepancies in the reported values of coercive fields and saturation polarization persist in literature for many materials. This raises questions about the atomic-scale mechanisms behind polarization reversal. Unconventional ferroelectric switching in ϵ-Fe2O3 films, a material that combines ferrimagnetism and ferroelectricity at room temperature, is reported here. High-resolution in-situ scanning transmission electron microscopy (STEM) experiments and first-principles calculations demonstrate that polarization reversal in ϵ-Fe2O3 occurs around pre-existing domain walls only, triggering local domain wall motion in moderate electric fields of 250 - 500 kV/cm. Calculations indicate that the activation barrier for switching at domain walls is nearly a quarter of that corresponding to the most likely transition paths inside ϵ-Fe2O3 domains. Moreover, domain walls provide symmetry lowering, which is shown to be necessary for ferroelectric switching. Local polarization reversal in ϵ-Fe2O3 limits the macroscopic ferroelectric response and offers important hints on how to tailor ferroelectric properties by domain structure design in other relevant ferroelectric materials.
@article{arxiv.1908.09691,
title = {Unconventional Ferroelectric Switching via Local Domain Wall Motion in Multiferroic $\epsilon$-Fe2O3 Films},
author = {Xiangxiang Guan and Lide Yao and Konstantin Z. Rushchanskii and Sampo Inkinen and Richeng Yu and Marjana Ležaić and Florencio Sánchez and Martí Gich and Sebastiaan van Dijken},
journal= {arXiv preprint arXiv:1908.09691},
year = {2019}
}