  The implementation of an Fe buffer layer is a promising way to obtain
epitaxial growth of Co-doped BaFe2As2 (Ba-122). However, the crystalline
quality and the superconducting properties of Co-doped Ba-122 are influenced by
the Fe buffer layer thickness, dFe. The well-textured growth of the Fe/Ba-122
bilayer with dFe = 15 nm results in a high Jc of 0.45 MAcm$^{-2}$ at 12 K in
self-field, whereas a low Jc value of 61000 Acm$^{-2}$ is recorded for the
bilayer with dFe = 4 nm at the corresponding reduced temperature due to the
presence of grain boundaries.
