5,272 research outputs found
Theoretical studies of spin-dependent electronic transport in ferromagnetically contacted graphene flakes
Based on a tight-binding model and a recursive Green's function technique,
spin-depentent ballistic transport through tinny graphene sheets (flakes) is
studied. The main interest is focussed on: electrical conductivity, giant
magnetoresistance (GMR) and shot noise. It is shown that when graphene flakes
are sandwiched between two ferromagnetic electrodes, the resulting GMR
coefficient may be quite significant. This statement holds true both for zigzag
and armchair chiralities, as well as for different aspect (width/length)
ratios. Remarkably, in absolute values the GMR of the armchair-edge graphene
flakes is systematically greater than that corresponding to the zigzag-edge
graphene flakes. This finding is attributed to the different degree of
conduction channel mixing for the two chiralities in question. It is also shown
that for big aspect ratio flakes, 3-dimensional end-contacted leads, very much
like invasive contacts, result in non-universal behavior of both conductivity
and Fano factor.Comment: to appear in PR
Large anisotropy in the optical conductivity of YNi2B2C
The optical properties of YNiBC are studied by using the
first-principles full-potential linearized augmented plane wave (FLAPW) method
within the local density approximation. Anisotropic behavior is obtained in the
optical conductivity, even though the electronic structure shows 3D character.
A large peak in is obtained at 2.4 eV. The anisotropic optical
properties are analyzed in terms of interband transitions between energy levels
and found that the Ni site plays an important role. The electronic energy loss
spectroscopy (EELS) spectra are also calculated to help elucidate the
anisotropic properties in this system.Comment: revtex4, 4 pages, 5 figures, to appear in PR
Orbital magnetism in the half-metallic Heusler alloys
Using the fully-relativistic screened Korringa-Kohn-Rostoker method I study
the orbital magnetism in the half-metallic Heusler alloys. Orbital moments are
almost completely quenched and they are negligible with respect to the spin
moments. The change in the atomic-resolved orbital moments can be easily
explained in terms of the spin-orbit strength and hybridization effects.
Finally I discuss the orbital and spin moments derived from X-ray magnetic
circular dichroism experiments
Interface properties of the NiMnSb/InP and NiMnSb/GaAs contacts
We study the electronic and magnetic properties of the interfaces between the
half-metallic Heusler alloy NiMnSb and the binary semiconductors InP and GaAs
using two different state-of-the-art full-potential \textit{ab-initio}
electronic structure methods. Although in the case of most NiMnSb/InP(001)
contacts the half-metallicity is lost, it is possible to keep a high degree of
spin-polarization when the interface is made up by Ni and P layers. In the case
of the GaAs semiconductor the larger hybridization between the Ni- and
As- orbitals with respect to the hybridization between the Ni- and P-
orbitals destroys this polarization. The (111) interfaces present strong
interface states but also in this case there are few interfaces presenting a
high spin-polarization at the Fermi level which can reach values up to 74%.Comment: 9 pages, 9 figure
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