Large in-plane anisotropies in Co/Re superlattices: What’s happening at the interface?

Journal of Applied Physics

et al. 2007

Self Cite

Structural, magnetotransport, and micromagnetic properties of sputtered Ir(111)/Co superlatticesThe structure and composition of a Co/ Re trilayer and a 19-period superlattice were characterized by high-resolution transmission electron microscopy ͑TEM͒ and scanning TEM ͑STEM͒. Low-angle x-ray reflectivity measurements were performed and compared with the TEM results. The Re and Co layers are epitaxial with their ͑1010͒ planes parallel to the ͑1120͒ plane of Al 2 O 3 , and the ͓001͔ direction of Re and Co layers coincides with that of the Al 2 O 3 . The in-plane lattice parameters for Co, Re, and Al 2 O 3 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 Al 2 O 3 corresponds to a / 2 and c / 3, where a and c are lattice parameters of the Al 2 O 3 . 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 Re/ Co 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.

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Structural and compositional characterization of a Co∕Re multilayer and superlattice

Journal of Applied Physics

et al. 2007

Self Cite

Atomic-scale structural analyses of epitaxial Co∕Re superlattices

Applied Physics Letters

et al. 2004

High-resolution transmission electron microscopy and scanning transmission electron microscopy (STEM) have been used to investigate atomic-scale structural properties of Co∕Re trilayers and superlattices grown via magnetron sputtering. The sample growth was epitaxial with the (101¯0) plane of Co and Re parallel to the (112¯0) plane of Al2O3, and the [001] direction of Re and Co coinciding with that of the Al2O3. Both low-angle and high-angle Z-contrast STEM images show a very uniform layer thickness. However, the interface roughness between the Re and Co layers monotonically increases with interface distance from the substrate. These results strongly imply that, in the epitaxial Re∕Co superlattice system, interface roughness plays a more important role in the giant magnetoresistance effect than thickness fluctuations of the spacer layer. Previous anisotropic magnetoresistance measurements can be explained in terms of the observed atomic-scale structure.

Structure Analysis of Co/Re Superlattice Grown on an Al₂O₃ (110) Substrate

et al. 2003

MRS Proc.

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.