[en] Quadruple perovskites with the bcc CaCu₃Ti₄O₁₂ crystal structure are becoming interesting for unusual magnetic, electronic, dielectric, and structural properties. It is shown here that the magnetic Cu d_xy states have unusual interrelationships (in terms of a tight binding representation) that have important implications for magnetic coupling. (author)

[en] In polycrystalline samples of superconducting MgCNi₃, the critical temperature and the specific heat were measured as a function of magnetic field. A Wertheimer-Helfand-Hohenberg (WHH)-like shape of H_c2(T) is observed. The H_c2(T) and specific heat data are discussed on a qualitative level in terms of effective single- and multi-band models based on an orbital assignment of the disjoint Fermi surface sheets (FSS) derived from LDA full potential electronic structure calculations

[en] The puzzle of three-dimensional magnetic interactions in the structurally two-dimensional layered-oxide Na_xCoO₂ is addressed using first-principles calculations and an analysis of the exchange mechanisms. The calculations agree with recent neutron results, favoring the antiferromagnetic stacking of ferromagnetic planes. The superexchange via direct O-O hopping and through intermediate Na sp² hybrids couples each Co to its nearest and six next-nearest interplanar neighbors via equivalent paths. The individual exchange constants are rather two-dimensional, like the lattice itself, but due to multiple c-axis exchange paths, the magnetism becomes effectively three-dimensional.

[en] We report here an order of magnitude enhancement of strength of sputter deposited Al/Al_2O_3 multilayers after annealing. The increase in strength is shown to be mostly associated with the precipitation of extremely fine γ-Al_2O_3, 5–10 nm in diameter, in Al layers. This provides a new method of achieving high strength in Al/Al_2O_3 multilayers that cannot be explained by the Koehler effect or modified Hall–Petch, which will lead to the growth and development of new generation of Al/Al_2O_3 multilayers. We also examine the fracture behavior of the post annealed Al/Al_2O_3 multilayered composites with TEM and density functional theory (DFT) simulations. DFT showed that the multilayers are not likely to delaminate at the Al/Al_2O_3 interface, consistent with the experimental observations. The simulations are also used to determine elastic constants for the γ-Al_2O_3 phase and to calculate a driving force for O transport from the γ-Al_2O_3 to the Al layers. The formation of these precipitates is consistent with DFT calculations, which predict an energetic driving force for the dissolution of O atoms from the γ-Al_2O_3 layers into the Al layers

No abstract available