Spin Wave Excitations in Topological Semimetal Mn₃Ga

Topological semimetals Mn₃X (X = Sn, Ge, Ga) are of interest for their exotic transport properties and potential application to spintronics technology. The interaction between the topological electronic states and the collective magnetic order is of particular importance. The properties of Mn₃Ga differ from Mn₃Sn and Mn₃Ge, for instance Mn₃Ga has been observed to display a significant spontaneous magnetization at low temperatures (0.2 μ_B/Mn [1]). Here we report what we believe to be the first inelastic neutron scattering results on hexagonal Mn₃Ga single crystals obtained with the SEQUOIA time-of-flight spectrometer at ORNL using incident neutron energies E_i = 40 meV, 150 meV, and 225 meV. We find dispersive magnetic excitations with a bandwidth exceeding 100 meV at T = 5 K. We use these to develop an effective low energy spin Hamiltonian and to evaluate trends in the character of the magnetic excitations across the Mn₃X series of compounds.

[1] H. Niida, T. Hori, and Y. Nakagawa, Magnetic Properties and Crystal Distortion of Hexagonal Mn₃Ga, J Physical Soc Japan 52, 1512 (1983).