Spin excitations of magnetoelectric LiNiPO${}_4$ in multiple magnetic phases

Abstract

Spin excitations of magnetoelectric LiNiPO${}_4$ 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, electric-dipole active, or magnetoelectric, 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.

References in corpus (4)

• Spin-stretching modes in anisotropic magnets: spin-wave excitations in the multiferroic Ba2CoGe2O7
• Field-induced magnetic phases and electric polarization in LiNiPO4
• Anomalous spin-waves and the commensurate-incommensurate magnetic phase transition in LiNiPO4
• Microwave directional dichroism resonant with spin excitations in the polar ferromagnet GaV${}_4$S${}_8$