Abstract
We have studied magnetic excitations in a field-induced noncollinear commensurate ferrimagnetic phase of by means of polarized inelastic neutron scattering (PINS) and terahertz (THz) time-domain optical spectroscopy under magnetic field. A previous THz spectroscopy study reported that the field-induced phase exhibits electric-dipole-active excitations with energies of around 5 meV [Kida et al., Phys. Rev. B 83, 064422 (2011)]. In the present PINS measurements, we observed inelastic scattering signals around 5 meV at the zone center in the spin-flip channel. This directly shows that the electric-dipole-active excitations are indeed of magnetic origin, that is, electromagnons. In addition, the present THz spectroscopy confirms that the excitations have oscillating electric polarization parallel to the axis. In terms of the spin-current model (Katsura-Nagaosa-Balatsky model), the noncollinear magnetic order in the field-induced phase can induce static electric polarization perpendicular to the axis, but not dynamic electric polarization along the axis. We suggest that the electromagnon excitations can be explained by applying the magnetostriction model to the out-of-phase oscillations of the magnetic moments, which is deduced from the present experimental results.
- Received 26 August 2015
- Revised 25 November 2015
DOI:https://doi.org/10.1103/PhysRevB.93.035119
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