Using a scattering matrix approach, the precession of the magnetization of a ferromagnet is shown to transfer spins into adjacent normal metal layers. This ``pumping'' of spins slows down the precession corresponding to an enhanced Gilbert damping factor in the Landau-Lifshitz equation. The damping is expressed in terms of the scattering matrix of the ferromagnet-normal metal interface, which is accessible to model and first-principles calculations. Our estimates for permalloy thin films explain the trends observed in recent experiments.
@article{arxiv.cond-mat/0110247,
title = {Enhanced Gilbert Damping in Thin Ferromagnetic Films},
author = {Yaroslav Tserkovnyak and Arne Brataas and Gerrit E. W. Bauer},
journal= {arXiv preprint arXiv:cond-mat/0110247},
year = {2009}
}