Magnon damping as a probe of Kondo coupling in magnetically ordered systems

In d-electron systems, there can also be intricate interplay between Kondo coupling and magnetic interactions as that in f-electron systems, but the underlying mechanism remains elusive. Here, using inelastic neutron scattering, we investigate the temperature evolution of the low-energy spin waves (magnons) in a metallic van der Waals ferromagnet Fe3−xGeTe2, and observe that the magnon damping diverges at both low and high temperatures and exhibits a minimum at an intermediate temperature. These behaviors are described by a formula that combines logarithmic and power-law terms, representing the dominant contributions from Kondo coupling and thermal fluctuations, respectively. These findings can be explained by considering electron-magnon scattering of spin-flip type within the ferromagnetic Kondo-Heisenberg lattice model, distinct from the original Kondo effect which only considers the coupling between itinerant electrons and isolated impurity spins. These results unveil the intriguing interplay between itinerant electrons and spin waves in metallic 3d-electron systems with magnetic order, and provide magnon damping as a new effective probe of Kondo coupling in metallic quantum magnets, thereby opening new avenues for exploring Kondo physics from the magnon perspective. While previous studies of Kondo physics have largely focused on electronic properties, the authors here investigate magnon damping in the d-electron van der Waals magnet Fe3GeTe2. They observe logarithmic scaling of the damping at low temperatures and a minimum at an intermediate temperature, which they attribute to Kondo coupling between itinerant electrons and local moments.