Functional Materials for Energy

Fundamental interactions of multiferroic BiFeO3

The spectroscopic modes of BiFeO3 in a magnetic field. Triangles and circles are data points for the different orientations of the THz magnetic and electric fields. Solid and dashed curves are predictions for the lowest-energy and higher-energy magnetic domains.

The agreement between the measured and predicted terahertz (THz) excitations indicates that a microscopic model can provide the foundation for future work on BiFeO3, which is the only known room-temperature multiferroic.  Due to the coupling between their electric and magnetic properties, mutliferroics would offer several advantages in magnetic storage devices and sensors. For data storage, information could be written electrically and read magnetically without heating by an electric current.   For sensors and actuators, providing a link between magnetic and electric fields would enable novel device concepts.

The spectroscopic modes of BiFeO3 provide detailed information about the very small interactions that produce the long-wavelength magnetic cycloid below 640 K.  A microscopic model now predicts the zero-field modes as well as their splitting and evolution in a magnetic field H along a cubic axis (see figure).  While the three magnetic domains of the cycloid have the same energy in zero field, THz measurements imply that the higher-energy domains are depopulated above about 6 T, indicated by a vertical line in the figure.  This direct link between computational and experimental results demonstrates the power of the microscopic model and provides the foundation for work on other multiferroics.

U. Nagel, R. S. Fishman, T. Katuwal, H. Engelkamp, D. Talbayev, H. T. Yi, S.-W. Cheong, and T. Rõõm, “Terahertz Spectroscopy of Spin Waves in Multiferroic BiFeO3 in High Magnetic Fields,” Phys. Rev. Lett. 110, 257201 (2013).

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