L. Peedu, V. Kocsis, D. Szaller, J. Viirok, U. Nagel, T. Rõõm, D. G. Farkas, Sándor Bordács, Dmytro Kamenskyi, U. Zeitler, Y. Tokunaga, Y. Taguchi, Y. Tokura, István Kézsmárki
- Spin excitations of magnetoelectric LiNiPO4 are studied by infrared absorption spectroscopy in the THz spectral range as a function of magnetic field through various commensurate and incommensurate magnetically ordered phases up to 33 T. Six spin resonances and a strong two-magnon continuum are observed in zero magnetic field. Our systematic polarization study reveals that some of the excitations are usual magnetic-dipole active magnon modes, while others are either electromagnons, being only electric-dipole active, or magnetoelectric, that is both electric- and magnetic-dipole active spin excitations. Field-induced shifts of the modes for all three orientations of the field along the orthorhombic axes allow us to refine the values of the relevant exchange couplings, single-ion anisotropies, and the Dzyaloshinskii-Moriya interaction on the level of a four-sublattice mean-field spin model. This model also reproduces the spectral shape of the two-magnon absorption continuum, found to beSpin excitations of magnetoelectric LiNiPO4 are studied by infrared absorption spectroscopy in the THz spectral range as a function of magnetic field through various commensurate and incommensurate magnetically ordered phases up to 33 T. Six spin resonances and a strong two-magnon continuum are observed in zero magnetic field. Our systematic polarization study reveals that some of the excitations are usual magnetic-dipole active magnon modes, while others are either electromagnons, being only electric-dipole active, or magnetoelectric, that is both electric- and magnetic-dipole active spin excitations. Field-induced shifts of the modes for all three orientations of the field along the orthorhombic axes allow us to refine the values of the relevant exchange couplings, single-ion anisotropies, and the Dzyaloshinskii-Moriya interaction on the level of a four-sublattice mean-field spin model. This model also reproduces the spectral shape of the two-magnon absorption continuum, found to be electric-dipole active in the experiment.…