Electrical control of electromagnons in BiFeO₃

The coupling between ferroelectric and magnetic order in multiferroic BiFeO3 enables the electrical control of magnetism [1], which is applicable for magneto-electric spin-orbit devices [2] and relevant to magnon current transport [3]. Despite numerous studies of magnetism in BiFeO3, there is still lack of understanding how magnons can be manipulated via an electric field. Specifically, it is essential to investigate magnons at finite momentum transfer Q to fully comprehend the magneto-electric coupling Hamiltonian.

Here, we conduct Fe L-edge resonant inelastic X-ray scattering (RIXS) combined with an in-situ electrical setup to uncover the changes in magnons under an electric field. We verified that a capacitor-like BiFeO3 device made from a single crystal exhibits ferroelectric polarization switching at an electric field of 15 kV/cm. Its switching is confirmed by linear dichroism changes in both X-ray absorption and RIXS spectra. The linear relation between the magnon energy shift at finite Q and the electric field resembles the trend of electromagnons previously observed in Raman [4]. On the other hand, the detected larger energy shift (~5 meV) in the magnon at Q=(0.1, 0, 0.3) and E=40 kV/cm compared to one observed in Raman (<1 meV) may indicate the sensible momentum dependence or an alternative mechanism of magneto-electric coupling. Our results provide unambiguous evidence of electrical control of magnons and a deeper understanding of the magneto-electric coupling in BiFeO3.

[1] A. Fert, R. Ramesh, V. Garcia, F. Casanova, and M. Bibes, Rev. Mod. Phys. 96, 015005 (2024)

[2] S. Manipatruni et al., Nature 565, 35 (2019)

[3] P. Meisenheimer et al., Adv. Mater. 36, 2404639 (2024)

[4] P. Rovillain et al., Nat. Mater. 9, 975 (2010)