In-plane anisotropy in the van der Waals antiferromagnet FePSe3 probed by magneto-Raman scattering

Magnon gap excitations selectively coupled to phonon modes have been studied in FePSe3 layered antiferromagnet with magneto-Raman-scattering experiments performed at different temperatures. The bare magnon excitation in this material has been found to be split (by approximate to 1.2 cm-1) into two components each being selectively coupled to one of the two degenerate, nearby phonon modes. Lifting the degeneracy of the fundamental magnon mode points out toward the biaxial character of the FePSe3 antiferromagnet, with an additional in-plane anisotropy complementing much stronger, out-of-plane anisotropy. Moreover, the tunability, with magnetic field and temperature, of the phonon-versus the magnon-like character of the observed coupled modes has been demonstrated.