Magneto-spectroscopy methods have been employed to study the zero-wavevector
magnon excitations in MnPSe3. Experiments carried out as a function of
temperature and the applied magnetic field show that two low-energy magnon
branches of MnPSe3 in its antiferromagnetic phase are gapped. The
observation of two low-energy magnon gaps (at 14 and 0.7 cm−1) implies
that MnPSe3 is a biaxial antiferromagnet. A relatively strong out-of-plane
anisotropy imposes the spin alignment to be in-plane whereas the spin
directionality within the plane is governed by a factor of 2.5 ×
10−3 weaker in-plane anisotropy.Comment: 9 pages, 3 figure