Controllable intrinsic Gilbert damping in Pt buffered [Co/Ni]n multilayers with enhanced perpendicular magnetic anisotropy

Abstract We systematically investigate the magnetization precession processes of post-prepared and after-annealing Pt buffered [Co/Ni]n multilayers with adjustable perpendicular magnetic anisotropy (PMA) by time-resolved magneto-optical Kerr effect. The PMA of the [Co/Ni]n multilayers could be modulated by changing the number of Co/Ni periods n, Pt thickness tPt and annealing temperature Ta, respectively. With a fixed tPt, both uniaxial magnetic anisotropy Ku and intrinsic damping constant α0 could be modulated by the variation of n. We observed that α0 is linearly proportional to Ku, since both of them originate from the spin-orbit coupling (SOC). For a fixed n, with the increase of tPt, Ku exhibits a non-monotonic change behavior, but α0 increases monotonously. It is found that α0 shows a nonlinear positve correlation to Ku. It suggests that the SOC is not the only factor affecting the damping process. Finally, for the specific sample, both α0 and Ku also display the different variation behaviors with increasing Ta. In this case, the changes in film microstructure caused by the annealing have different contributions to Ku and α0, resulting in a negative correlation between Ku and α0. The findings could be helpful to design the potential application of [Co/Ni]n multilayers system in STT-MRAM with high density, low power and high thermal stability.