Interacting spin waves in the ferromagnetic Kondo lattice model

We present an new approach for the ferromagnetic, three-dimensional, translational-symmetric Kondo lattice model which allows us to derive both magnon energies and linewidths (lifetimes) and to study the properties of the ferromagnetic phase at finite temperatures. Both "anomalous softening" and "anomalous damping" are obtained and discussed. Our method consists of mapping the Kondo lattice model onto an effective Heisenberg model by means of the "modified RKKY interaction" and the "interpolating self-energy approach". The Heisenberg model is approximatively solved by applying the Dyson-Maleev transformation and using the "spectral density approach" with a broadened magnon spectral density.