Preparation and structural characterization of epitaxial Co/Pd(111) superlattices

Abstract

High-quality epitaxial fcc Co/Pd(111) superlattices have been prepared on single-crystal GaAs(110) substrates using molecular-beam epitaxy. An ultrathin (6 Å) buffer layer of bcc Co(110) was used to promote epitaxial growth on the GaAs substrate. A thick (≊ 500 Å) buffer layer of fcc Pd(111) was then deposited to provide a smooth surface for superlattice growth. In addition, the Pd buffer layer isolates the superlattice from chemical interaction with the GaAs substrate. Co/Pd superlattices with ultrathin (<20 Å) Co layers are found to have a perpendicular easy axis of magnetization. The source of the perpendicular magnetization in these superlattices is attributed to an interface anisotropy, which depends on the interface quality and crystal structure. The structure of the superlattices has been investigated using a wide range of techniques, including reflection high- energy electron diffraction, low-energy electron diffraction, scanning tunneling microscopy, Rutherford backscattering spectroscopy, and a variety of x-ray-diffraction techniques. Details of the structure, including grain size, coherence length, and interfacial roughness are discussed. The magnetic properties of these superlattices are presented elsewhere in these proceedings.