First-principles prediction of coexistence of magnetism and ferroelectricity in rhombohedral Bi2FeTiO6

TL;DR

This study uses first-principles calculations to predict that rhombohedral Bi2FeTiO6 is a multiferroic material exhibiting both magnetism and ferroelectricity, with potential applications in multifunctional devices.

Contribution

It is the first to theoretically demonstrate coexistence of magnetism and ferroelectricity in Bi2FeTiO6 using density functional theory with LSDA+U.

Findings

Rhombohedral Bi2FeTiO6 is a potential multiferroic.

Spontaneous polarization of 27.3 μC/cm² was calculated.

Ferromagnetic configuration with 4 μB per formula unit was identified.

Abstract

First principles calculations based on the density functional theory within the local spin density approximation plus U(LSDA+U)scheme, show rhombohedral Bi$_2$FeTiO$_6$ is a potential multiferroic in which the magnetism and ferroelectricity coexist . A ferromagnetic configuration with magnetic moment of 4 $\mu_B$ per formula unit have been reported with respect to the minimum total energy. Spontaneous polarization of 27.3 $\mu$ C/cm$^2$, caused mainly by the ferroelectric distortions of Ti, was evaluated using the berry phase approach in the modern theory of polarization. The Bi-6s stereochemical activity of long-pair and the `d$^0$-ness' criterion in off-centring of Ti were coexisting in the predicted new system. In view of the oxidation state of Bi$^{3+}$,Fe$^{2+}$,Ti$^{4+}$, and O$^{2-}$ from the orbital-resolved density of states of the Bi-6p, Fe-3d,Ti-3d, and O-2p states,the valence state of Bi$_2$FeTiO$_6$ in the rhombohedral phase was found to be Bi$_2$$^{3+}$Fe$^{2+}$Ti$^{4+}$O$_6$.