  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.
