In fabrication of magnetic spin valves and magnetic tunnel junctions (MTJ), ruthenium is extensively used as a means of coupling antiferromagnetically the magnetization in two ferromagnetic layers. Elemental cobalt has a high magnetostriction, which makes its use as an electrode in spintronic devices unsatisfactory. However, by alloying it with iron this is dramatically reduced and an 80% Co20% Fe composition is very commonly used. Further, although Co and Ru are miscible, when cobalt is alloyed with iron the chemical affinity between the two reduces the miscibility with ruthenium [1] and the interfaces are expected to be relatively sharp.The stability of the interface structure of sputtered Ru/Co80Fe20 layers during high temperature annealing has been studied recently [2] using grazing incidence X-ray scattering and interfaces have been shown to be stable up to at least 400◦ C. In this paper, we examine the interface structure of Ru/Co80Fe20 multilayers in more detail.