Abstract
(langasite) is structurally and magnetically single-domain chiral with the magnetic helicity induced through competing symmetric exchange interactions. Using neutron scattering, we show that the spin waves in antiferromagnetic langasite display directional anisotropy. On applying a time-reversal symmetry breaking magnetic field along the axis, the spin-wave energies differ when the sign is reversed for either the momentum transfer or applied magnetic field . When the field is applied within the crystallographic plane, the spin-wave dispersion is directionally isotropic and symmetric in . However, a directional anisotropy is observed in the spin-wave intensity. We discuss this directional anisotropy in the dispersion in langasite in terms of a field-induced precession of the dynamic unit cell staggered magnetization resulting from a broken twofold symmetry. Directional anisotropy, often referred to as nonreciprocal responses, can occur in antiferromagnetic phases in the absence of the Dzyaloshinskii-Moriya interaction or other effects resulting from spin-orbit coupling.
- Received 20 June 2019
- Revised 30 August 2019
DOI:https://doi.org/10.1103/PhysRevB.100.134429
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