All-optical study of the influence of Co and W stacking sequence on magnetization precession and damping and magnetic anisotropy in asymmetric Pt/(W,Co)/Pt heterostructures

The influence of the Co- and W-layer stacking sequence and the Co-layer thickness d Co on the magnetization precession and damping and magnetic anisotropy is investigated using the all-optical time-resolved magneto- optical Kerr (TRMOKE) effect in asymmetric Pt/W/Co/Pt and Pt/Co/W/Pt heterostructures prepared by molecular beam epitaxy. It is found that the reversing of the stacking sequence of the Co and W layers leads to significant changes in the magnetic-field H dependencies of the magnetization precession frequency f and the effective damping parameter alpha eff for different d Co thicknesses. A quantitative analysis of the f (H) dependencies is carried out within the macrospin precession model, and the effective magnetic anisotropy constants K eff are determined. It is shown that, in addition to the first-order coefficient K 1 , also the second-order K 2 uniaxial anisotropy constant must be taken into account for the Pt/Co/W/Pt stack, while K 2 is insignificant for the reversed Pt/W/Co/Pt stack. From the K eff ( d Co ) dependencies, the interface K s and volume K v anisotropy contributions for all heterostructures are obtained. The value of K s = 1.24 mJ/m2 for the Pt/Co/W/Pt stack is found to be over two times larger as compared to K s = 0.55 mJ/m2 for the Pt/W/Co/Pt one. The interfacial anisotropy induced at the bottom Pt/Co interface in the Pt/Co/W/Pt heterostructure is shown to be significantly larger than that induced at the top Co/Pt interface in the Pt/W/Co/Pt stack. From the effective damping parameter alpha eff ( H ) dependencies, the intrinsic damping alpha 0 is extracted, and the interface-induced damping contributions to alpha 0 within the spin-pumping model are derived. It is found that the effective spin-mixing conductance parameter g up arrow down arrow eff for the Pt/Co/W/Pt structure exceeds 100 nm-2 and is about two times larger than for the Pt/W/Co/Pt one, indicating the dominant Pt/Co-bottom interface contribution to the spin-pumping damping. A correlation between the intrinsic damping alpha 0 and anisotropy constant K 1 for all layered structures studied is found and discussed in terms of the dependence of both quantities on the spin-orbit coupling. It is shown that the magnetic anisotropy parameters determined from the dynamic TRMOKE method agree well with those obtained from complementary measurements performed using the static magneto-optical Kerr effect.