Anisotropic magnetic interactions in hexagonal A B -stacked kagome lattice structures: Application to Mn 3 X ( X = Ge , Sn , Ga ) compounds

Mn3X compounds in which the magnetic Mn atoms form AB-stacked kagome lattices have received a tremendous amount of attention since the observation of the anomalous Hall effect in Mn3Ge and Mn3Sn. Although the magnetic ground state has been known for some time to be an inverse triangular structure with an induced in-plane magnetic moment, there have been several controversies about the minimal magnetic Hamiltonian. We present a general symmetry-based model for these compounds that includes a previously unreported interplane Dzyaloshinskii-Moriya interaction, as well as anisotropic exchange interactions. The latter are shown to compete with the single-ion anisotropy which strongly affects the ground state configurations and elementary spin-wave excitations. Finally, we present the calculated elastic and inelastic neutron scattering intensities and point to experimental assessment of the types of magnetic anisotropy in these compounds that may be important.