Unconventional Ferroelectric Switching via Local Domain Wall Motion in Multiferroic $\epsilon$-Fe2O3 Films

TL;DR

This study reveals that in $ ext{ε}$-Fe₂O₃ films, ferroelectric polarization reverses specifically at domain walls, involving local domain wall motion triggered by moderate electric fields, which influences the material's macroscopic ferroelectric behavior.

Contribution

It uncovers the atomic-scale mechanism of ferroelectric switching in $ ext{ε}$-Fe₂O₃, showing domain wall motion as the key process, supported by high-resolution microscopy and first-principles calculations.

Findings

Polarization reverses at pre-existing domain walls.

Activation barrier for switching at domain walls is significantly lower.

Domain walls enable symmetry lowering necessary for ferroelectric switching.

Abstract

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 $\epsilon$-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 $\epsilon$-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 $\epsilon$-Fe2O3 domains. Moreover, domain walls provide symmetry lowering, which is shown to be necessary for ferroelectric switching. Local polarization reversal in $\epsilon$-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.