Origin of increase of damping in transition metals with rare-earth-metal impurities.

The damping due to rare-earth-metal impurities in transition metals is discussed in the low concentration limit. It is shown that all established damping mechanisms based on spin-orbit and/or spin-spin interactions cannot explain experimental observations even qualitatively. We introduce a different relaxation channel due to the coupling of the orbital moments of the rare-earth-metal impurities and the conduction p electrons that leads to good agreement with experiment. Using an itinerant picture for the host ions, i.e., write their magnetization in terms of the electronic degrees of freedom, is key to the success of our model.