Structure Analysis of Co/Re Superlattice Grown on an Al 2 O 3 (110) Substrate
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L11.31.1
Structure Analysis of Co/Re Superlattice Grown on an Al2O3 (110) Substrate Wentao Xu1, Timothy Charlton2, 3, Lance E. De Long1, David Lederman3 Department of Physics and Astronomy, University of Kentucky, Lexington, KY 40506, USA 2 Materials Science Division, Argonne National Laboratory, Argonne, IL 60439, USA 3 Department of Physics, West Virginia University, Morgantown, WV 26506, USA 1
ABSTRACT The structure of a Re(5 nm)/(Co(2 nm)/Re(3 nm))19 sample grown via magnetron sputtering was thoroughly analyzed via x-ray reflectivity (XRR) and transmission electron microscopy (TEM). Cross-sectional TEM results indicate that the sample is epitaxial, with the in-plane c-axis of the superlattice pointing along the c-axis of the substrate. A quantitative analysis of XRR yielded an average thickness of each layer and an interface roughness ~ 0.4 nm between the Co and Re layers. A careful analysis of the TEM data reveals that the in-plane lattice parameters for Co, Re and Al2O3 are approximately 0.24 nm, 0.43 nm; 0.26 nm, 0.44 nm; and 0.24 nm, 0.44 nm, respectively. The lattice spacings of Al2O3 correspond to a/2 and c/3, where a, and c are lattice parameters, respectively. Interestingly, both high resolution and Z-contrast images show a very uniform period thickness. Z-contrast images, however, show that the initial interface roughness between the Re buffer layer and the first Co layer is amplified as the layers get farther away from the substrate. A high magnification TEM analysis shows that the bottom Co-Re interface roughness is about 0.2 nm, whereas the top Re-Co interface roughness is about 0.7 nm. Previous anistropic magnetoresistance measurements are discussed in light of these new structural data. INTRODUCTION The giant magnetoresistance (GMR) of magnetic multilayers has attracted dramatic attention both from the point of view of basic physics and for applications such as high-sensitivity reading heads and magnetic sensors. In magnetic multilayer systems, GMR depends only on the relative orientation of the magnetic moments of the layers. In most of these structures, the layer thicknesses are much less than an electronic mean free path but much longer than the spin relaxation length. Therefore, for homogeneous layers, spin-dependent scattering at interfaces plays a primary importance in understanding the nature of GMR results. Perfectly smooth interfaces would give rise to only specular scattering, which would generate no interfacial impedance. However, in a real system, it is very difficult to determine the role of the interfaces played in the electron scattering process. In some multilayer systems, the GMR is reported to depend on the interface roughness1, 2, but other studies show that the GMR depends on the thickness fluctuation of spacer layers between magnetic film layers3, 4. The Co/Re epitaxial superlattice system combines GMR together with anisotropic magnetoresistance (AMR). We have reported that this system has unusual transport properties; in particular, the GMR and AMR can compete or reinforce e
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