Investigation of Room Temperature Ferroelectricity and Ferrimagnetism in Multiferroic AlxFe2-xO3 Epitaxial Thin Films

TL;DR

This study demonstrates room temperature ferrimagnetism in AlxFe2-xO3 epitaxial thin films and explores their potential ferroelectric properties, revealing challenges due to domain structure and defects, with implications for multiferroic device applications.

Contribution

The paper reports the successful deposition of low-leakage AlxFe2-xO3 thin films exhibiting room temperature ferrimagnetism and investigates their ferroelectric behavior through experiments and first-principles calculations.

Findings

Confirmed room temperature ferrimagnetism in AlxFe2-xO3 films

Predicted high polarization from calculations, but observed lower polarization experimentally

Oxygen vacancies facilitate polarization switching by aiding domain wall motion

Abstract

Multiferroic materials open up the possibility to design novel functionality in electronic devices, with low energy consumption. However, there are very few materials that show multiferroicity at room temperature, which is essential to be practically useful. AlxFe2-xO3 (x-AFO) thin films, belonging to the k-Al2O3 family are interesting because they show room temperature ferrimagnetism and have a polar crystal structure. However, it is difficult to realise its ferroelectric properties at room temperature, due to low resistivity of the films. In this work, we have deposited x-AFO (0.5 <= x <= 1) epitaxial thin films with low leakage, on SrTiO3<111> substrates by Pulsed Laser Deposition. Magnetic measurements confirmed room temperature ferrimagnetism of the films, however the Curie temperature was found to be influenced by deposition conditions. First principle calculations suggested that ferroelectric domain switching occurs through shearing of in-plane oxygen layers, and predicted a high polarization value of 24 uC/cm2. However, actual ferroelectric measurements showed the polarization to be two order less. Presence of multiple in-plane domains which oppose polarization switching of adjacent domains, was found to be the cause for the small observed polarization. Comparing dielectric relaxation studies and ferroelectric characterization showed that oxygen-vacancy defects assist domain wall motion, which in turn facilitates polarization switching.