Using first principles density functional calculations, we study the electronic structure of the low-dimensional multiferroic compound FeTe${}_2$O${}_5$Br to investigate the origin of the magnetoelectric (ME) effect and the role of Te ions in this system. We find that without magnetism, even in the presence of Te 5$s$ lone pairs, the system remains centrosymmetric due to the antipolar orientation of the lone pairs. Our study shows that the exchange striction within the Fe tetramers as well as between them is responsible for the ME effect in FeTe${}_2$O${}_5$Br. We also find that the Te${}^{4+}$ ions play an important role in the intertetramer exchange striction as well as contributing to the electric polarization in FeTe${}_2$O${}_5$Br, once the polarization is triggered by the magnetic ordering.

• Received 28 June 2013

DOI:https://doi.org/10.1103/PhysRevB.88.094409