Period of oscillatory exchange interactions in Co/Cu and Fe/Cu multilayer systems

Abstract

A simple expression is presented for the period Λ of oscillatory interlayer exchange interactions in Co/X and Fe/X magnetic multilayer systems (X= a nearly-free-electron metal). Λ is shown to be much longer than the period λ of the Ruderman-Kittel-Kasuya-Yosida-like spin-density oscillations in the X layers, which are induced by the coupling with the ferromagnetic layers, if λ is close to an integral fraction of the interlayer spacing in the X layers. The dependence of Λ on the growth direction of the multilayers is explained. From the available experimental data on fcc Co/Cu(111), fcc Co/Cu(100), and fcc Fe/Cu(100), and from results of recently published band-structure calculations for bcc Fe/Cu(100) effective values of λ have been derived. In some cases small but significant deviations were found from the value of λ which is predicted from the Ruderman-Kittel-Kasuya-Yosida theory.