First-principles study of the Gilbert damping constants of Heusler alloys based on the torque correlation model

On the basis of the torque correlation model for the Gilbert damping constant α, we perform the first principles calculation for α for Co-based Heusler alloys, Co2MnAl (CMA), Co2MnSi (CMS), and Co2FeSi (CFS). In the ordered (L21) and partially disordered (B2) structures, the calculated values of α reflect half-metallicity or the gap structure around the Fermi level, EF, i.e. CMS with 100% spin-polarization has the smallest value. The valence electron number dependence of α follows the experimental trend. However, the calculated values are almost a factor of ten smaller than the measured ones. Although the α values are larger in the completely disordered (A2) structure, they are not as large as the experimental results. Therefore, the decreasing degree of order or the breakdown of the half-metallicity is not responsible for the discrepancy.