NMR analysis of buried metallic interfaces

Owing to the sensitivity of the hyperfine field to the topological and chemical environment of the probe nuclei, NMR spectra can be considered as detailed histograms of the short range order ruling the structure of the material under investigation. Complementary to diffraction techniques this gives a local insight into the structure in the direct space. We present here recent developments of the method which have been used for structural investigations of cobalt layers imbedded in Co/X multilayers and particularly of buried interfaces. Indeed the use of spectrum modelling allows a detailed, quantitative, description of the way intermixing takes place at the interfaces. Co/Cu multilayers, a case of weakly miscible elements, have been specially investigated. Such a case is the most likely to yield sharp interfaces. Actually, the interface structure is shown to depend drastically on the preparation conditions and techniques, resulting in very different interfaces from abrupt to largely mixed. Solid solution forming elements (Co/Ru or Co/Cr) have also been studied for which interdiffusion at the interfaces is more expected. Indeed thick diffusion profiles, across several atomic planes, are observed which are much less dependent on the preparation technique than in the former case. The case of compound forming elements (Co/Fe) shows the largest interface admixture with a structure that seems also reminiscent of the bulk alloy phase diagram.