Multiferroic materials are important because their electrical and magnetic properties are coupled. Because BiFeO3 magnetically orders below 640 K, it is one of two known room-temperature multiferroic materials. Recently, theorists at Oak Ridge National Laboratory discovered that the spin-driven electric polarization of BiFeO3 below its magnetic ordering temperature, TN, is much larger than in any other known multiferroic.
The spin-driven polarization below TN is produced by the rotation of the FeO6 octahedron and points opposite to the even larger pre-existing electric polarization above TN. Ironically, the large size of the pre-existing polarization has prevented direct observation of the giant spin-driven polarization. However, recent neutron diffraction measurements of the crystal parameters confirm the theoretical predictions, as shown in the figure.
This giant spin-driven polarization will allow the development of devices that control the magnetic properties of BiFeO3 with an electric field or control its electric properties with a magnetic field. The theoretical technique developed in this work can also be used to study the spin-driven electric polarizations in other technologically important multiferroic materials.
Jun Hee Lee and Randy S. Fishman, “Giant Spin-Driven Ferroelectric Polarization in BiFeO3 at Room Temperature,” Phys. Rev. Lett. 115, 207203 (2015). DOI: 10.1103/PhysRevLett.115.207203
For more information, contact Randy Fishman: firstname.lastname@example.org