Spin excitations in the Kagome antiferromagnet YFe₆Sn₆

Kagome materials exhibit may intriguing properties in the electronic states related to their magnetic states. For the Kagome family 𝑅𝑇6Sn6, most of them have a ferromagnetic ground state, only YFe6Sn6 is found to be an antiferromagnet below TN=551 K. There appears a weak ferromagnetism resulted from the spin reorientation at low temperatures associated with an anomalous Hall effect. Our recent neutron scattering experiments on YFe6Sn6 single crystals confirm the antiferromagnetic state and observe strong spin excitations below 300 K. A unique Y-shape dispersion of the magnetic excitations is observed both in [H, K]-plane and along L direction, where the incommensurate branches emerge above about 10 meV. Below 10 meV, the magnetic excitations are highly temperature dependent. There are two types of excitations circling around Q=(1, 0) and (2, 0) (or Q=(0, 0)) , respectively. While both of them mostly present at L= 0.5 and 1.5, the former has a much weaker intensity and only appears below 50 meV, the latter shows a ring-like dispersions up to 160 meV . These results suggest that the spin dynamics in YFe6Sn6 may be contributed both by FM and AF interactions, but they may compete with each other at different temperatures. More importantly, the excitations around Q=(1, 0) probably is a signature of chiral magnon in such Kagome lattice.