Research Highlight

Giant Spin-Driven Electric Polarization is Revealed in Promising Multiferroic

Comparison between the predicted and observed spin-driven polarization (above) and of the octahedral rotation angle qAFD (below) are shown as a function of temperature. The contribution from exchange striction (ES) dominates those from single-ion anisotropy (SIA) and spin current (SC).

Multiferroic materials are important because their electrical and magnetic properties are coupled.  Because BiFeO3 magnetically

Comparison between the predicted and observed spin-driven polarization (above) and of the octahedral rotation angle AFD (below) are shown as a function of temperature. The contribution from exchange striction (ES) dominates those from single-ion anisotropy (SIA) and spin current (SC). Comparison between the predicted and observed spin-driven polarization (above) and of the octahedral rotation angle AFD (below) are shown as a function of temperature. The contribution from exchange striction (ES) dominates those from single-ion anisotropy (SIA) and spin current (SC). (hi-res image)
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:  fishmanrs@ornl.gov

 

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