Fe/Ba(Fe1−xCox)2As2 multilayers and quasi-multilayers with Tc = 29 K

In this work we present multilayers consisting of Fe and Co-doped BaFe2As2 fabricated by UHV pulsed laser deposition. Employing the advantage of a coherent interfacial bonding between the FeAs tetrahedra of the iron pnictide and bcc Fe enables the growth of epitaxial bi- and multilayers of Fe and the new Fe-based superconductors with high crystalline quality. Epitaxial growth of the multilayers was controlled in situ by reflection high energy electron diffraction (RHEED) and after film growth by X-ray diffraction and TEM analysis. The stoichiometry determined by Auger electron spectroscopy (AES) indicated As-deficient layers of Co-doped Ba-122. The multilayers exhibit critical temperatures of Tc,90 = 29 K which is so far the highest critical temperature reported for Co-doped Ba-122. We propose that the Tc-enhancement is caused by As-vacancies.