Antiferromagnetic magnon gap opening and spin-reorientation in Li-doped MnTe

MnTe emerges as a promising platform for ultra-fast carrier dynamics, spin-based thermoelectrics, and topological insulators. We investigate the impact of spin waves of a doping-driven transition of hexagonal MnTe from an easy-plane to an easy-axis antiferromagnet. Using inelastic neutron scattering, we reveal the emergence of enhanced magnetic anisotropy upon Li-doping, which leads to the opening of a magnon gap. The origin of this magnon gap in Li-doped MnTe is attributed to the enhanced c-axis magnetic anisotropy, a phenomenon absent in pure MnTe. This enhanced c-axis anisotropy in doped MnTe is also substantiated by Linear spin-wave theory and density functional theory calculations.