Magnetic anisotropy of Fe_xCo_1-x multilayers on Cu(001): Reorientation transition of magnetic moments due to different interlayer coupling

The magnetic anisotropy energies of Fe_xCo_1-x multilayers on Cu(001) have been determined by means of ab initio calculations using the fully relativistic, spin-polarized screened Korringa-Kohn-Rostoker method within the local spin density approximation. By utilizing the coherent potential approximation the Fe/Co system was treated within a mean-field approach as a (uniform) randomly disordered alloy. The type of magnetic interlayer coupling—either ferromagnetic or antiferromagnetic—that is energetically more favorable is found to depend on both the film thickness and alloy composition. It seems therefore that the type of magnetic interlayer coupling is also responsible for the reorientation transition mainly because of the strong enhancement of the band energy contribution to the magnetocrystalline anisotropy energy in the case of antiferromagnetic coupling.