The electric transport properties of Fe/X s /Fe model systems have been investigated for current perpendicular to the plane geometry. Three different spacer materials XϭGe, ͓In, P͔, ͓Zn, Se͔ have been used in order to examine the dependence of the magnetoresistance with respect to the spacer thickness. In the case of binary spacer materials the influence of the termination of the spacer material is also investigated. In addition, some important technical aspects like the variation of the sheet

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... esistance with the number of lead layers are discussed. The investigations have been performed in the framework of the relativistic spin-polarized version of the screened Korringa-Kohn-Rostoker method, and the Kubo-Greenwood formula has been used to describe the transport properties. It has been observed that for all three systems the magnetoresistance becomes constant with increasing spacer thickness, the absolute value depending on the material and the termination of the spacer. Furthermore, we can demonstrate that the dominant contributions to the magnetoresistance arise from the Fe/X and X/Fe interfaces.