Magnetic anisotropy in epitaxial Co superlattices

A series of epitaxial Co-Au and Co-Cu superlattices has been grown by molecular-beam-epitaxy techniques, with Co thicknesses varying from 5 to 40 \AA{} and constant Au and Cu thicknesses of 16 and 25 \AA{}, respectively. We compare the magnetic properties of both types of superlattice. Crossover to an easy axis normal to the film plane occurs at a thickness of 19 \AA{} of Co in the Co-Au series and 10 \AA{} of Co in the Co-Cu series. We show that the observed magnetic behavior of both of these systems can be accounted for by contributions from demagnetization, magnetocrystalline anisotropy, and magnetoelastic anisotropy. The magnetoelastic term depends on the strain present in Co layers, which in turn is a function of the Co-layer thickness. In our calculation we employ measured Co-layer strains, determined by x-ray scattering, in combination with the known elastic and magnetostriction constants of bulk Co.