Multiferroic Bi$_2$NiMnO$_6$ Thin Films: A Computational Prediction

TL;DR

This study uses first-principles calculations to challenge previous reports about bulk Bi2NiMnO6's ferroelectricity, predicting it can become a ferroelectric ferromagnet when grown as an epitaxial film on specific substrates.

Contribution

It provides the first computational prediction that Bi2NiMnO6 is not ferroelectric in bulk but can be engineered into a ferroelectric ferromagnet as an epitaxial film.

Findings

Bulk Bi2NiMnO6 is centrosymmetric with no polarization.

Epitaxial growth on certain substrates induces ferroelectric ferromagnetism.

Predicted conditions for ferroelectricity include specific substrate lattice constants.

Abstract

We report first-principles calculations for one of the few materials that is believed to be a ferroelectric ferromagnet, Bi$_2$NiMnO$_6$. Our calculations show that, contrary to what it has been reported so far, bulk Bi$_2$NiMnO$_6$ does not have a polarization. Instead, like BiMnO$_3$, it crystallizes into a centrosymmetric structure with space group $C2/c$. We also predict that Bi$_2$NiMnO$_6$ will indeed be a ferroelectric ferromagnet if it is grown as an epitaxial film on a substrate with in-plane square symmetry and a lattice constant around 4~\AA, such as BaTiO$_3$ or PbZr$_{1-x}$Ti$_{x}$O$_{3}$.