Growth and x-ray scattering studies of epitaxial cobalt superlattices.

In this thesis we describe the MBE growth and x-ray scattering analysis of magnetic Co-Au and Co-Cu superlattices. The superlattices are epitaxially ordered in that the in-plane crystallographic orientation of individual layers is preserved throughout the growth process, as shown by in-situ reflection high energy electron diffraction (RHEED) studies. This epitaxial ordering is confirmed by x-ray scattering measurements performed in transmission, with the scattering vector parallel to the plane of the superlattice. In addition, these x-ray measurements determine the in-plane epitaxial strains in the superlattice layers. These strains are useful in estimating magnetoelastic contributions to the magnetic anisotropy. The composition modulation in the growth direction has been analyzed via x-ray scans performed with the scattering vector normal to the film plane. The measured intensities have been compared to computer simulations which incorporate interfacial diffusion and layer thickness fluctuations. We find that the interfaces in these superlattices are limited in thickness to a 2 monolayer region. Finally, x-ray scans along 101$\ell$ are used to distinguish hcp and fcc stacking sequences in Co layers. We find that, in the case of Co-Au superlattices, the Co planes are stacked according to the hcp sequence (which is stable in the bulk below 400$\sp\circ$C). However, in Co-Cu superlattices, the Co planes are stacked according to the fcc sequence, providing an example of the epitaxial stabilization of a structure which does not occur in the bulk under ambient conditions.