  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.
