Multiple magnon modes in the Co$_3$Sn$_2$S$_2$ Weyl semimetal candidate

We experimentally investigate electron transport in kagome-lattice ferromagnet Co$_3$Sn$_2$S$_2$, which is regarded as a time reversal symmetry broken Weyl semimetal candidate. We demonstrate $dV/dI(I)$ curves with pronounced asymmetric $dV/dI$ spikes, similar to those attributed to current-induced spin-wave excitations in ferromagnetic multilayers. In contrast to multilayers, we observe several $dV/dI$ spikes' sequences at low, $\approx$10$^4$ A/cm$^2$, current densities for a thick single-crystal Co$_3$Sn$_2$S$_2$ flake in the regime of fully spin-polarized bulk. The observed behavior necessarily requires a distinct magnetic structure with a small total spin value, so we attribute $dV/dI$ spikes to multiple magnon branches in Co$_3$Sn$_2$S$_2$ Weyl surface states. We demonstrate splitting of the magnon branches in high magnetic fields, which may reflect reconstruction of spin textures in the surface state due to the spin-momentum locking. Presence of spin-transfer effects at low current densities in Co$_3$Sn$_2$S$_2$ makes the material attractive for applications in spintronics.