Magnetic anisotropy and damping for monolayer-controlled Co | Ni epitaxial multilayer

Structures and magnetic properties were systematically investigated for the monolayer (ML)-controlled Co | Ni multilayers with various Ni layer thicknesses, where the Co and Ni layers were epitaxially grown on a Al₂O₃ (1120) single crystal substrate or deposited on a thermally oxidized Si substrate. The epitaxial Co | Ni multilayers exhibited high uniaxial magnetic anisotropy energies (K_u) and low effective magnetic damping constants (α_eff), resulting in the perpendicular magnetization with low damping even for the 1 ML-Ni | 1 ML-Co multilayer. By comparing the experimental results with the first principles calculation, we found that the Ni atoms largely contributed to the perpendicular anisotropy for the Co | Ni multilayers. We also discussed the possible mechanism dominating the magnitude of α_eff for the Co | Ni multilayers based on the experiments and the calculations. The present results suggest that the epitaxial Co | Ni multilayer is a promising material to achieve high K_u and low magnetic damping simultaneously.