FUNDAMENTAL OSCILLATION PERIODS OF THE INTERLAYER EXCHANGE COUPLING BEYOND THE RKKY APPROXIMATION

A general method for obtaining the oscillation periods of the interlay er exchange coupling is presented. It is shown that it is possible for the coupling to oscillate with additional periods beyond the ones pre dicted by the RKKY theory. The relation between the oscillation period s and the spacer Fermi surface is clarified, showing that non-RKKY per iods do not bear a direct correspondence to the Fermi surface. The int eresting case of an FCC(110) structure is investigated, unmistakably p roving the existence and relevance of non-RKKY oscillations. The gener al conditions for the occurrence of non-RKKY oscillations are also pre sented.