274 research outputs found
Tunneling conductance of graphene ferromagnet-insulator-superconductor junctions
We study the transport properties of a graphene ferromagnet-insulator
superconductor (FIS) junction within the Blonder-Tinkham-Klapwijk formalism by
solving spin-polarized Dirac-Bogoliubov-de-Gennes equation. We find that the
retro and specular Andreev reflections in the graphene FIS junction are
drastically modified in the presence of exchange interaction and that the
spin-polarization () of tunneling current can be tuned from the positive
to negative value by bias voltage (). In the thin-barrier limit, the
conductance of a graphene FIS junction oscillates as a function of barrier
strength . Both the amplitude and phase of the conductance oscillation
varies with the exchange energy . For (Fermi energy), the
amplitude of oscillation decreases with . For ,
the amplitude of oscillation increases with , where
( is the applied electrostatic potential on
the superconducting segment of the junction). For , the
amplitude of oscillation decreases with again. Interestingly, a
universal phase difference of in exists between the
curves for and . Finally, we find that the transitions
between retro and specular Andreev reflections occur at and
, and hence the singular behavior of the conductance near
these bias voltages results from the difference in transport properties between
specular and retro Andreev reflections.Comment: Accepted for publication in Physical Review
Carrier-induced ferromagnetism in n-type ZnMnAlO and ZnCoAlO thin films at room temperature
The realization of semiconductors that are ferromagnetic above room
temperature will potentially lead to a new generation of spintronic devices
with revolutionary electrical and optical properties. Transition temperatures
in doped ZnO are high but, particularly for Mn doping, the reported moments
have been small. We show that by careful control of both oxygen deficiency and
aluminium doping the ferromagnetic moments measured at room temperature in
n-type ZnMnO and ZnCoO are close to the ideal values of 5mB and 3mB
respectively. Furthermore a clear correlation between the magnetisation per
transition metal ion and the ratio of the number of carriers to the number of
transition metal donors was established as is expected for carrier induced
ferromagnetism for both the Mn and Co doped films. The dependence of the
magnetisation on carrier density is similar to that predicted for the
transition temperature for a dilute magnetic semiconductor in which the
exchange between the transition metal ions is through the free carriers.Comment: 14 pages pd
European Core Health Indicators - status and perspectives.
The European Core Health Indicators (ECHI) are a key source of comparable health information for the European Union (EU) and its Member States (MS). The ECHI shortlist contains 88 indicators which were developed by experts from MS and international organisations. Most indicators are derived from data sources at the EU's statistical office (Eurostat), the World Health Organisation (WHO) and the Organisation for Economic Co-operation and Development (OECD) and are available for most MS. The remaining indicators on the shortlist are at different stages of conceptual and/or methodological development. The indicators have been reviewed in the past against scientific developments, changes in data collections and emerging policy needs, yet not as part of a systematic and sustainable procedure. There is also no regular inventory of problems met by the MS in collecting the necessary data. Work package 4 of the BRIDGE Health project aimed at updating and improving the existing ECHI-indicator knowledge and expertise and at strengthening the scientific base that supports the effective development and use of health indicators for health policy evaluation and prioritization by the EU and its MS. The aim of this paper is to present a first overview of its outcomes and to explore issues concerning the ECHI data availability, content and policy relevance, update process and accessibility to stakeholders, in light of working towards a sustainable future
Calculations of giant magnetoresistance in Fe/Cr trilayers using layer potentials determined from {\it ab-initio} methods
The ab initio full-potential linearized augmented plane-wave method
explicitly designed for the slab geometry was employed to elucidate the
physical origin of the layer potentials for the trilayers nFe/3Cr/nFe(001),
where n is the number of Fe monolayers. The thickness of the transition-metal
ferromagnet has been ranged from up to n=8 while the spacer thickness was
fixed to 3 monolayers. The calculated potentials were inserted in the
Fuchs-Sondheimer formalism in order to calculate the giant magnetoresistance
(GMR) ratio. The predicted GMR ratio was compared with the experiment and the
oscillatory behavior of the GMR as a function of the ferromagnetic layer
thickness was discussed in the context of the layer potentials. The reported
results confirm that the interface monolayers play a dominant role in the
intrinsic GMR.Comment: 17 pages, 7 figures, 3 tables. accepted in J. Phys.: Cond. Matte
Operationally Efficient Propulsion System Study (OEPPS)
A description is presented, through view graphs, of the problems encountered in today's launch vehicles and how these problems have adversely affected the ability to achieve serviceability, reliability, and operability. The need is emphasized to recognize and understand the operations problems and the effort that must be made to avoid them in future designs. Technology areas that will enhance operations requirements are also presented
Grain boundary effects on magnetotransport in bi-epitaxial films of LaSrMnO
The low field magnetotransport of LaSrMnO (LSMO) films
grown on SrTiO substrates has been investigated. A high qualtity LSMO film
exhibits anisotropic magnetoresistance (AMR) and a peak in the
magnetoresistance close to the Curie temperature of LSMO. Bi-epitaxial films
prepared using a seed layer of MgO and a buffer layer of CeO display a
resistance dominated by grain boundaries. One film was prepared with seed and
buffer layers intact, while a second sample was prepared as a 2D square array
of grain boundaries. These films exhibit i) a low temperature tail in the low
field magnetoresistance; ii) a magnetoconductance with a constant high field
slope; and iii) a comparably large AMR effect. A model based on a two-step
tunneling process, including spin-flip tunneling, is discussed and shown to be
consistent with the experimental findings of the bi-epitaxial films.Comment: REVTeX style; 14 pages, 9 figures. Figure 1 included in jpeg format
(zdf1.jpg); the eps was huge. Accepted to Phys. Rev.
Vortex lattices in strong type-II superconducting two-dimensional strips
We show how to calculate semi-analytically the dense vortex state in strong
type-II superconducting nanostructures. For the specific case of a strip, we
find vortex lattice solutions which also incorporate surface superconductivity.
We calculate the energy cost to displace individual vortex rows parallel to the
surfaces and find that this energy oscillates with the magnetic field.
Remarkably, we also find that, at a critical field below , this
''shear'' energy becomes strictly zero for the surface rows due to an
unexpected mismatch with the bulk lattice.Comment: Title, abstract, and some text paragraphs have been rewritte
Development and Application of 3-Dimensional Transmission Electron Microscopy (3D-TEM) for the Characterization of Metal-Zeolite Catalyst Systems
With electron tomography (3D-TEM) a 3D-reconstruction is calculated from a series of
TEM images taken at a tilt angle range (tilting range) of +70° to -70°. The reconstruction can
be visualized with contour surfaces that give information about the surface of the sample as
well as with slices through the reconstruction that give detailed information on the interior of
the sample. Electron tomography gives much more information than Scanning Electron
Microscopy (SEM), since SEM gives only information about the surface of a sample. As a
case study, the imaging of silver clusters on zeolite NaY is given. The reconstruction shows
silver particles at the external surface as well as a silver particle in a mesopore of the zeolite
crystallite. It is concluded that 3D-TEM comprises a breakthrough in the characterization of
nano-structured solid catalysts
Room temperature magneto-optics of ferromagnetic transition-metal doped ZnO thin films
Magneto-optic studies of ZnO doped with transition metals Co, Mn, V and Ti
indicate a significant magnetic circular dichroism (MCD) at the ZnO band edge
at room temperature, together with an associated dispersive Faraday rotation.
Similar spectra occur for each dopant which implies that the ferromagnetism is
an intrinsic property of the bulk ZnO lattice. At 10 K additional paramagnetic
contributions to the MCD are observed, but above about 150K, the magnitude of
the MCD signal is dominated by the ferromagnetism and is almost temperature
independent. The MCD at the ZnO band edge shows room temperature hysteretic
behaviour.Comment: 4 page
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