Extremely large perpendicular magnetic anisotropy of an Fe(001) surface capped by 5d transition metal monolayers: A density functional study

Significant enhancement of the magnetocrystalline anisotropy (MCA) of an Fe(001) surface capped by 4d and 5d transition metal monolayers is presented in this study using first principles density functional calculations. In particular, an extremely large perpendicular MCA of +10 meV/Ir was found in Ir-capped Fe(001), which originates not from the Fe but from the large spin-orbit coupling of the Ir atoms. From the spin-channel decomposition of the MCA matrix and electronic structure analyses, we find that strong 3d-5d band hybridization in the minority spin state is responsible for the sign changes of the MCA from parallel to perpendicular.open0

Do Nest Materials and Nest Substrates affect the Breeding of \u3ci\u3eButeo hemilasius\u3c/i\u3e in the Mongolian Steppe?

Upland buzzards occur across Mongolia excluding lush taiga forest and breeds from the Mongolian Altai mountains to the western foothills of the Great Khyangan Mountains. Our field work was conducted during the breeding season of the species in Mongolia from 2001 to 2007. Nest materials of the studied nests contained natural (twigs of elm tree, shrubs, tail, and mane of horse, hair of cows, fur of sheep, goats and camels), and artificial or man-made (cotton, plastic bags, wires, cables, and others) materials. Contents of the nesting materials of the species were differed by location, region and breeding pair’s behavior. A total of 24 different nest sites were selected by breeding pairs during the study periods. Most nests were placed on the ground (22.7%), 19.7% on artificial nest platforms (three-legged poles, single poles, car tire on poles, pylons), 16.8% on rocky outcrops, 8.8% on rocky columns or cliffs, 5.26% on type A wooden poles of high power electric lines and 26.74% others. Average clutch was comparatively high for breeding pairs that nested on rock columns 3.9, abandoned buildings 3.7, ground 3.6, cliffs 3.3, type “A” wooden poles of the high power electric lines 3.3, sandy precipice 3 and others less than three. Average number of nestlings on the ruins of buildings was 3, rock columns 2.8, ground, telegraph poles and concrete poles of the high power electric lines 2.5, wooden poles of the high power electric lines and pylons 2.4, well building and livestock shelter 2, cliffs 1.6 and sandy precipices 1.5. There was a significant difference between the number of nestlings on natural and artificial substrates, including artificial nest platforms. We documented a breeding pair that was incubating three of its own eggs and a Saker falcon egg on a cliff of a mountain outcrop. We also observed twice the number of second clutches on natural substrates, which we consider to be dependent on food abundance and accessibility

Ultrahard carbon film from epitaxial two-layer graphene

Atomically thin graphene exhibits fascinating mechanical properties, although its hardness and transverse stiffness are inferior to those of diamond. To date, there hasn't been any practical demonstration of the transformation of multi-layer graphene into diamond-like ultra-hard structures. Here we show that at room temperature and after nano-indentation, two-layer graphene on SiC(0001) exhibits a transverse stiffness and hardness comparable to diamond, resisting to perforation with a diamond indenter, and showing a reversible drop in electrical conductivity upon indentation. Density functional theory calculations suggest that upon compression, the two-layer graphene film transforms into a diamond-like film, producing both elastic deformations and sp2-to-sp3 chemical changes. Experiments and calculations show that this reversible phase change is not observed for a single buffer layer on SiC or graphene films thicker than 3 to 5 layers. Indeed, calculations show that whereas in two-layer graphene layer-stacking configuration controls the conformation of the diamond-like film, in a multilayer film it hinders the phase transformation.Comment: Published online on Nature Nanotechnology on December 18, 201

Si doped T6 carbon structure as an anode material for Li-ion batteries: An ab initio study

First-principles calculations are performed to identify the pristine and Si doped 3D metallic T6 carbon structure (having both sp(2) and sp(3) type hybridization) as a new carbon based anode material. The pi electron of C-2 atoms (sp2 bonded) forms an out of plane network that helps to capture the Li atom. The highest Li storage capacity of Si doped T6 structure with conformation Li1.7Si1C5 produces theoretical specific capacity of 632 mAh/g which substantially exceeding than graphite. Also, open-circuit voltage (OCV) with respect to Li metal shows large negative when compared to the pristine T6 structure. This indicates modifications in terms of chemical properties are required in anode materials for practical application. Among various doped (Si, Ge, Sn, B, N) configuration, Si doped T6 structure provides a stable positive OCV for high Li concentrations. Likewise, volume expansion study also shows Si doped T6 structure is more stable with less pulverization and substantial capacity losses in comparison with graphite and silicon as an anode materials. Overall, mixed hybridized (sp(2) + sp(3)) Si doped T6 structure can become a superior anode material than present sp2 hybridized graphite and sp(3) hybridized Si structure for modern Lithium ion batteries.ope

Intrinsic magnetism of an individual rare-earth atom on transition metal dichalcogenide semiconductors

Two-dimensional (2D) structures that exhibit intriguing magnetic phenomena such as perpendicular magnetocrystalline anisotropy (PMA) have become a focus of spintronic research due to their potentials in maximizing the information storage density. Herein we perform density-functional theory plus U (DFT+U) calculations to investigate the binding affinity and intrinsic magnetic properties of an individual rare-earth (RE) Sm atom on WSe2 monolayer. Our calculations show that Sm adatom energetically prefers to adsorb at the W-top site in WSe2 rather than the Se-top and hollow sites. We predict extremely large PMA values of ∼7–33 meV per Sm at the most stable W-top site, depending on U parameter in DFT+U calculations, while it is negligibly small for the Se-top and hollow sites. The underlying mechanism for large PMA is elucidated in terms of the strong spin–orbit coupled Sm 4f – W 5d orbital states and large 4f orbital magnetic moment in the high-spin crystal field. These results provide a viable route to achieving an atomic scale f-electron PMA in 2D structures, opening interesting prospects in two-dimensional semiconducting spintronics