Perpendicular Anisotropy and Gilbert Damping in Sputtered Co/Pd Multilayers

Gilbert damping constants α of Co/Pd multilayers with various layered structures were estimated by time resolved magneto-optical Kerr effect. The [Co(t_Co)/Pd(t_Pd)]₆ multilayers exhibiting a perpendicular magnetic anisotropy (PMA) were prepared by dc magnetron sputtering on a Pd (1 nm)/Ta (30 nm)/oxidized Si substrate. The PMA of the multilayer having t_Co/t_Pd=0.55 increased with decreasing the bilayer period, t_Co+t_Pd, while all the multilayers showed almost the same α of 0.09. The same trend was seen for Co/Ni multilayers with a constant t_Co/t_Ni, although the values of α are different, i.e., 0.035 for Co/Ni . From the estimation of the damping α of the multilayers with various t_Co/t_Pd, the α was confirmed to be enhanced when the ratio t_Co/t_Pd becomes lower than 0.8. Moreover, the linear relationship between the α and t_Pd/t_Co was found. These results suggest that the damping α of both Co/Pd and Co/Ni multilayers are not closely correlated with their PMA, and mainly determined by the composition of the multilayers.