Resonant x-ray reflectivity studies of Fe/Cr interfaces*

Eric E. Fullerton1, J. Bai1,2, and P. A. Montano1,3

1. Materials Science Division, Argonne National Laboratory
2. Brooklyn College of the City University of New York
3. University of Illinois, Chicago

We have measured the interfacial profiles in Fe/Cr superlattices by resonant
x-ray reflectivity.  Fe/Cr (001) and (112) superlattices were epitaxially
grown by magnetron sputtering onto single-crystal MgO (001) and (011)
substrates, respectively.  The two orientations were grown simultaneously
which allows a direct comparison of the interfacial profiles for different
crystallographic orientations.  Resonant reflectivity measurements were
carried out by tuning the x-ray energy around the respective K-edges of Fe and
Cr.  We then self consistently fit all data sets to the same structural model
to determine not only the electron density profiles but also the compositional
profiles.  Such information is normally difficult to obtain in reflectivity
measurements due to the low contrast between Fe and Cr.  The results are
compared to similar experiments on Cr films grown by molecular beam epitaxy
onto the (001) surface of a Fe whisker.  Fe whiskers are atomically smooth
over lateral length scales greater than 1 mm and provide a nearly perfect
substrate for the study of Cr growth on Fe.

* Work supported by the U.S. Department of Energy, Basic Energy
Sciences-Materials Sciences, under contract No. W-31-109-ENG-38.