8 research outputs found
Magnetic states of granular layered CoFe-Al\u3csub\u3e2\u3c/sub\u3eO\u3csub\u3e3\u3c/sub\u3e
The granular layered magnetic system Co80Fe20(t)/Al2 O3 (3 nm), where the Co80Fe20 layers of nominal thickness t form separate, almost spherical magnetic granules of typical diameter 2-3 nm between the Al2O3 spacers, was studied. We discuss measurements of the dc and ac magnetic susceptibility χ for 1 n
Substitutional doping of Cu in diamond: Mott physics with orbitals
Discovery of superconductivity in the impurity band formed by heavy doping of
boron into diamond (C:B) as well as doping of boron into silicon (Si:B) has
provided a rout for the possibility of new families of superconducting
materials. Motivated by the special role played by copper atoms in high
temperature superconducting materials where essentially Cu orbitals are
responsible for a variety of correlation induced phases, in this paper we
investigate the effect of substitutional doping of Cu into diamond. Our
extensive first principle calculations averaged over various geometries based
on density functional theory, indicates the formation of a mid-gap band, which
mainly arises from the and states of Cu. For impurity
concentrations of more than 2pt_{2g}4p\sim 5%, completely closes the
spectral gap of the host diamond.Comment: 5 figure
Low-temperature orientational ordering and possible domain structures in C₆₀
Based on a simple model for the ordering of hexagons on a square planar lattice, an attempt is made to consider the possible
structure of С₆₀ fullerite in its low-temperature phase. It is shown that hexagons representing fullerenes oriented along the С₃ axes of the sc lattice can be ordered into an ideal structure with four nonequivalent molecules in the unit cell. Then the energy degeneracy for the rotation of each hexagon by π/3 around its С₃ axis leaves the translational and orientational order in this structure but leads to a random distribution of π/3 rotations and hence to an “averaged” unit cell with two molecules. However, the most relevant structural defects are not these intrinsic “misorientations” but some walls between domains with different sequences of the above-mentioned two (nonideal) sublattices. Numerical estimates are made for the anisotropic intermolecular potential, showing that the anisotropy is noticeably smaller for molecules in walls than in domains
Resistive switching in nanostructured thin films
Planar capacitor structures based on granular films composed of nanometric ferromagnetic grains embedded in an insulating Al2O3 matrix can switch between a high-conductance and a low-conductance state. The switching properties are induced by a forming process. The ON/OFF resistance ratio is as high as 104 under an electrical field of only 15 kV/m. This resistive switching is accompanied by a capacitive switching between two well-defined voltage-independent states, a behavior that is not readily explained by the filamentary type of conduction