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 α0 increases continuously with increasing the Pd thickness tPd, showing no linear correlation with the perpendicular magnetic anisotropy constant Ku 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 Ku but larger α0, 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.