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arXiv · 1904.06106

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

Laur Peedu·Vilmos Kocsis·Dávid Szaller·Johan Viirok·Urmas Nagel·Toomas Rõõm·Dániel Gergely Farkas·Sándor Bordács·Dmytro Kamenskyi·Uli Zeitler·Yusuke Tokunaga·Yasujiro Taguchi·Yoshinori Tokura·István Kézsmárki
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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.

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Laur Peedu, Vilmos Kocsis, Dávid Szaller, Johan Viirok, Urmas Nagel, Toomas Rõõm, Dániel Gergely Farkas, Sándor Bordács, Dmytro Kamenskyi, Uli Zeitler, Yusuke Tokunaga, Yasujiro Taguchi, Yoshinori Tokura, István Kézsmárki. 2019-04-12. Spin excitations of magnetoelectric LiNiPO$_4$ in multiple magnetic phases. https://doi.org/10.1103/physrevb.100.024406

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