Microscopic Theory of Gilbert Damping for Transition Metal Systems

Abstract

We provide an overview on the microscopic theory of Gilbert damping and a theoretical framework to calculate the damping constant. In general, the damping constant can be expressed using the spin susceptibility of electronic system using the molecular field Hamiltonian. For a uniform magnetic dynamics (Kittel mode), magnetic damping does not occur unless the magnetic scatterings or spin-orbit interactions exist. Based on these concepts, we have performed the first principles calculation for the Gilbert damping constants  of transition metal systems such as Fe-Ni and Fe-Pt using the tight-binding linear muffin-tin orbital (TB-LMTO) method with inclusion of spin-orbit interactions. Quantitatively, the calculated  's are approximately half of the experimental values, whereas the variations in the Fermi level dependence of  are much larger than these discrepancies． As expected, we confirm that for (Fe-Ni)1-XPtX and FePt systems the Pt atoms enhance  due to their large spin-orbit coupling. For the disordered alloys, we find that  decreases with an increasing chemical degree of order in the wide range.