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

Abstract

Kagome-lattice materials have attracted tremendous interest due to the broad prospect for seeking superconductivity, 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 ${\mathrm{Fe}}_{0.89}{\mathrm{Co}}_{0.11}\mathrm{Sn}$. Although the magnetic excitations can be observed up to $\ensuremath{\sim}250$ meV, well-defined spin waves are only identified below $\ensuremath{\sim}90$ meV and can be modeled using Heisenberg exchange with ferromagnetic in-plane nearest-neighbor coupling ${J}_{1}$, in-plane next-nearest-neighbor coupling ${J}_{2}$, and antiferromagnetic (AFM) interlayer coupling ${J}_{c}$ under linear spin-wave theory. Above $\ensuremath{\sim}90$ 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 ${\mathrm{Fe}}_{0.89}{\mathrm{Co}}_{0.11}\mathrm{Sn}$, solve the magnetic Hamiltonian for both states, and confirm the significant influence of the itinerant magnetism on the spin excitations.