Phenomenological approach to the dependence of magnetic anisotropy on Co layer thickness in epitaxial Au/Co and Au/Co/Ag superlattices

Co-layer-thickness (t) dependences of magnetic anisotropy energies (K-eff) in epitaxial (111)Au/Co and (111)Au/Co/Ag superlattices are interpreted phenomenologically. Saturation of K-eff at small t in a t - K-eff plot is attributed to two nonidentical interfaces of each Co layer and the gradient of Co-layer in-plane strain in the thickness direction. The strains are estimated from the results of in situ reflection high-energy electron diffractometry, which were reported earlier, taking electron penetration to the near-surface regions into account. The magnetoelastic interface anisotropy contributing to the perpendicular magnetic anisotropy is suggested to arise from a larger magnetoelastic constant than that in bulk Co, which is in agreement with recent theoretical calculations.