Evidence for Room-Temperature Multiferroicity in a Compound with a Giant Axial Ratio

Abstract

In the search for multiferroic materials magnetic compounds with a strongly elongated unit-cell (large axial ratio $c/a$) have been scrutinized intensely. However, none was hitherto proven to have a switchable polarization, an essential feature of ferroelectrics. Here, we provide evidence for the epitaxial stabilization of a monoclinic phase of ${\mathrm{BiFeO}}_3$ with a giant axial ratio ($c/a=1.23$) that is both ferroelectric and magnetic at room temperature. Surprisingly, and in contrast with previous theoretical predictions, the polarization does not increase dramatically with $c/a$. We discuss our results in terms of the competition between polar and antiferrodistortive instabilities and give perspectives for engineering multiferroic phases.