Spin excitations in the kagome-lattice metallic antiferromagnet Fe0.89Co0.11Sn

Kagome-lattice materials have attracted tremendous interest due to the broad prospect for seeking supercon-ductivity, quantum spin liquid states, and topological electronic structures. Among them, the transition-metal kagome lattices are high-profile objects for the combination of topological properties, rich magnetism, and multiple-orbital physics. Here we report an inelastic neutron scattering study on the spin dynamics of a kagome-lattice antiferromagnetic metal Fe0.89Co0.11Sn. Although the magnetic excitations can be observed up to -250 meV, well-defined spin waves are only identified below -90 meV and can be modeled using Heisenberg exchange with ferromagnetic in-plane nearest-neighbor coupling J1, in-plane next-nearest-neighbor coupling J2, and antiferromagnetic (AFM) interlayer coupling Jc under linear spin-wave theory. Above -90 meV, the spin waves enter the itinerant Stoner continuum and become highly damped particle-hole excitations. At the K point of the Brillouin zone, we reveal a possible band crossing of the spin wave, which indicates a potential Dirac magnon. Our results uncover the evolution of the spin excitations from the planar AFM state to the axial AFM state in Fe0.89Co0.11Sn, solve the magnetic Hamiltonian for both states, and confirm the significant influence of the itinerant magnetism on the spin excitations.