Interlayer exchange coupling: Effect of the cap

The effect of nonmagnetic cap layers on the periods, amplitudes, and phases of the oscillations of the interlayer exchange coupling (IEC) is studied theoretically using ab initio methods. We employ the spin-polarized surface Green function technique within a tight-binding linear muffin-tin orbital method and the Lloyd formulation of the IEC. Application is made to Co/Cu/Co(001) trilayers with a Cu cap interfacing vacuum through the dipole barrier. We investigate in detail both an asymmetric case with one semi-infinite Co slab and the other Co slab being five monolayers thick and a symmetric case with Co slabs of monolayer thickness. In all cases we have found a pronounced oscillatory behavior of the amplitudes and the phases of the IEC oscillations as a function of the thickness of the cap. The case of different spacer and cap materials is also studied. The results for different spacer and different cap thicknesses are analyzed in terms of a discrete Fourier transformation as well as in real space, and found to confirm predictions by the electron confinement model on an ab initio level.