Ab initio calculations of interaction energies of magnetic layers in noble metals: Co/Cu(100)

We present ab initio calculations for the interlayer exchange coupling of magnetic Co(100) layers in Cu. The calculations are based on a Korringa-Kohn-Rostoker Green's function method for planar defects and apply the frozen potential approximation, allowing a direct calculation of the interaction via single-particle energies. Thus the subtraction of large total energies is avoided and efficient calculations for large layer thicknesses are enabled. By dividing the two-dimensional Brillouin zone into areas around different stationary points q(i), an analysis of the asymptotic behavior is given. The different dependences of the short and long oscillation periods on the thickness of the magnetic layers are explained by the q(parallel to)- and symmetry-projected density of states of the Co layers. The effects of roughness on the interlayer coupling are simulated, leading to a strong reduction of the amplitudes and a suppression of the short-wavelength period. Our calculations are in good agreement with experiments and give a consistent picture of interlayer coupling in Co/Cu(100), as far as both the dependence on the thickness of the magnetic layers as well as the dependence on roughness are concerned.