Magnetic damping and perpendicular magnetic anisotropy in Pd- buffered [Co/Ni]5 and [Ni/Co]5 multilayers

We systematically studied the influence of Pd underlayer on the magnetic properties of perpendicular [Co/Ni](5) and [Ni/Co](5) multilayers by time-resolved magneto-optical Kerr effect. We found that the saturated magnetic damping constant alpha(0) increases continuously with increasing the Pd thickness t(Pd), showing no linear correlation with the perpendicular magnetic anisotropy constant K-u for both series of samples. As compared to the Co/Ni sample with the same tPd, the Ni/Co film shows lower saturation magnetization, weaker K-u but larger alpha(0), which can be ascribed to the presence of more paramagnetic spins at the Pd/Ni interface due to the weak exchange coupling stiffness between Ni atoms. By analyzing extrinsic damping contributions from magnetic inhomogeneities, two-magnon scattering and spin pumping effects, the intrinsic damping of perpendicular [Ni/Co](5) is quantitatively determined to be 0.023. This study should provide deep understanding and effective control of magnetic damping for designing high performance magnetic memory devices.