Ab initiocalculations 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 ${\mathrm{q}}_i$, 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 ${\mathbf{q}}_{\mathrm{\parallel }}$- 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.