Lack of dependence between intrinsic magnetic damping and perpendicular magnetic anisotropy in Cu(t_Cu)/[Ni/Co]_N multilayers

The correlation between magnetic damping and perpendicular magnetic anisotropy has been investigated in Cu(t_Cu)/[Ni/Co]_N multilayers by time-resolved magneto-optical Kerr effect. The uniaxial magnetic anisotropy constant K_u is varied in the range of 3.0–3.6 Merg/cm³ by tuning either multilayer repetition number N or Cu thickness t_Cu. It is found that the PMA strength K_u increases with the increase of N, while the damping constant α₀ keeps nearly a constant of 0.025, implying the intrinsic damping is independent of the K_u tuned by N. In contrast, as t_Cu increases from 2.5 to 20 nm, the α₀ value rises continuously up to 0.040, in spite of the rather weak enhancement in K_u and its non-monotonic variation behavior. We consider the constant α₀ with N is due to the unchanged spin-orbit coupling strength at each Co/Ni interface, while the obvious enhancement in α₀ with t_Cu results mainly from the increased degree of spin disordering at the rougher Cu/Ni interface.