Theoretical Study of Gilbert Damping in Rare-Earth Permanent Magnets

We investigate temperature dependence of the Gilbert damping of a magnetization of the Fe sublattice in rare-earth permanent magnets R
₂
Fe
₁₄
B (R is a rare-earth element). Assuming that the spin angular moment of Fe dissipates to the phonon system via a localized 4f electron system, which interacts with the phonon system, we obtain the formulation of the Gilbert damping constant α on the basis of the ligand field theory and evaluate the temperature and material dependence of α. We show that the Gilbert damping of the magnetization arises only in certain temperature regions due to the discrete energy structure of the 4f electron system.