Abstract-Optical magnetoelectric resonance in a polar magnet (Fe,Zn)2Mo3O8 with axion-type coupling

T. Kurumaji, Y. Takahashi, J. Fujioka, R. Masuda, H. Shishikura, S. Ishiwata, and Y. Tokura

https://journals.aps.org/prl/accepted/e4078Y6fQc815163827c0719a8372934e33e6b2ac

We report the polarization rotation of terahertz light resonant with the magnetoelectric (ME) spin excitation in the multiferroic (Fe, Zn)2Mo3O8. This resonance reflects the frequency dispersion of the diagonal ME susceptibility (axion term), with which we quantitatively reproduce the thermal and magnetic-field evolution of the observed polarization rotation spectra. The application of the sum rule on the extrapolated DC value of the spectral weight of the ME oscillator provides insight into the DC linear ME effect. The present finding highlights a novel optical functionality of spin excitations in multiferroics that originates from diagonal ME coupling.

Abstracts-Electromagnon resonance in a collinear spin state of the polar antiferromagnet Fe2Mo3O8

T. Kurumaji, Y. Takahashi, J. Fujioka, R. Masuda, H. Shishikura, S. Ishiwata, and Y. Tokura

Phys. Rev. B 95, 020405(R) – Published 5 January 2017

https://journals.aps.org/prb/abstract/10.1103/PhysRevB.95.020405

Magnetic excitations are investigated for a hexagonal polar magnet Fe2Mo3O8 by terahertz spectroscopy. We observed magnon modes including an electric-field active magnon, electromagnon, in the collinear antiferromagnetic phase with spins parallel to the c axis. We unravel the nature of these excitations by investigating the correlation between the evolution of the mode profile and the magnetic transition from antiferromagnetic to ferrimagnetic order induced by a magnetic field or Zn doping. We propose that the observed electromagnon mode involves the electric polarization oscillating within the c plane induced by the collective precession of the spins through the same mechanism as producing the linear magnetoelectric effect.

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