  Motivated by recent experiments on molecular quantum dots we investigate the
relaxation of pure spin states when coupled to metallic leads. Under suitable
conditions these systems are well described by a ferromagnetic Kondo model.
Using two recently developed theoretical approaches, the time-dependent
numerical renormalization group and an extended ow equation method, we
calculate the real-time evolution of a Kondo spin into its partially screened
steady state. We obtain exact analytical results which agree well with
numerical implementations of both methods. Analytical expressions for the
steady state magnetization and the dependence of the long-time relaxation on
microscopic parameters are established. We find the long-time relaxation
process to be much faster in the regime of anisotropic Kondo couplings. The
steady state magnetization is found to deviate significantly from its thermal
equilibrium value.
