Structural and compositional characterization of a CoRe multilayer and superlattice

The structure and composition of a CoRe trilayer and a 19-period superlattice were characterized by high-resolution transmission electron microscopy (TEM) and scanning TEM (STEM). Low-angle x-ray reflectivity measurements were performed and compared with the TEM results. The Re and Co layers are epitaxial with their (10 1- 0) planes parallel to the (11 2- 0) plane of Al2 O3, and the [001] direction of Re and Co layers coincides with that of the Al2 O3. The in-plane lattice parameters for Co, Re, and Al2 O3 are approximately 0.24 and 0.43 nm, 0.26 and 0.44 nm, and 0.24 and 0.44 nm, respectively, in the superlattice. The lattice spacing of Al2 O3 corresponds to a2 and c3, where a and c are lattice parameters of the Al2 O3. High-angle and low-angle annular-dark-field STEM and nanoscale electron energy loss spectroscopy line analysis exhibit very weak interdiffusion between Co and Re layers; therefore, very sharp interfaces are maintained in the superlattice. The initial interface roughness between the Re buffer layer and the first Co layer is amplified during the subsequent growth of the superlattices. Layer thickness fluctuations are much smaller in the ReCo superlattice than the interface roughness, which suggests that interface roughness plays a more important role in the giant magnetoresistance effect than thickness fluctuations of the spacer layer.