Chiral magnetic excitations in the RMn6Sn6 kagome metals (R=Tb, Ho, Er, and Y)

Recent inelastic neutron scattering (INS) investigations of the kagome metal TbMn6Sn6 reveal novel chiral magnetic excitations associated with the kagome layer. These excitations appear to have an itinerant character with a large energy scale (> 100 meV) and heavy damping; however, the origin of these excitations, which are not predicted by local moment linear spin-wave theory, is not understood. Here, we use INS to show that chiral excitations are also found in RMn6Sn6 compounds with R=Tb, Ho, Er, and Y having uniaxial, tilted, planar ferrimagnet, and planar double-spiral magnetic structures, respectively. Thus, the chiral excitations exist regardless of the magnetic structure. Additionally, R=Er and Y demonstrate that the chiral mode intensity is weaker in planar magnetic structures, suggesting that excitations are transverse to the local Mn moment direction. The chiral excitations appear only at L=odd positions in the Brilloun zone, and correspond to chiral spin exciations of the same handedness within each kagome layer, and pi out-of-phase between layers.