Magnetic damping in perpendicular [Pt/Co]3/MnIr multilayers

We studied the influence of Pt, Co and MnIr layer on the exchange bias field H_E and coercive field H_C in perpendicular exchange-biased [Pt/Co]₃/MnIr multilayers by magneto-optical Kerr effect. As the thickness of the Pt layer increases, the perpendicular magnetic anisotropy constant K_u first increases and then reaches to saturation, which is resulted from the competition between perpendicular anisotropy and interfacial short-range interaction. The saturation damping constant α₀ of the sample increases from about 0.062 to 0.122 when the Pt thickness increases from 0.5 nm to 1.5 nm. However, α₀ increases with the decrease of Co thickness. We attributed both of these mainly to spin pumping effect.