Spin dynamics of the isotropic kagome ferromagnet Fe₃Sn₂

The giant anomalous Hall effect in the itinerant kagome magnet Fe₃Sn₂ was recently attributed to massive Dirac fermions resulting in a Berry curvature in the ferromagnetic phase [1], with a topologically non-trivial field-dependent spin texture phase discovered[2], demonstrating an intimate relationship between the electronic and magnetic properties in this strongly correlated electron material. Here we present a new perspective on Fe₃Sn₂ by studying the magnetic excitations near q=0 using inelastic neutron scattering. The results on polycrystalline samples show this material to be an isotropic ferromagnet near its T_C of 660 K, where we find a negligible spin gap, and large spin-wave stiffness. The moments initially point along the c-axis and slowly rotate over the course of several hundred degrees towards the ab-plane. This indicates the “soft” nature of the ferromagnet, which is at odds with the argument that anisotropy is responsible for some the materials’ properties elsewhere in phase space. Additionally, magnetic susceptibility and magnetization measurements agree with our neutron diffraction results showing this sample does not undergo a re-entrant spin-glass phase as reported by some.
[1] Ye, et al. Nature 555, 638 (2018); [2] Hou, et al. Adv. Mater. 29, 1701144 (2017).