878 research outputs found
Magnetoresistance of atomic-sized contacts: an ab-initio study
The magnetoresistance (MR) effect in metallic atomic-sized contacts is
studied theoretically by means of first-principle electronic structure
calculations. We consider three-atom chains formed from Co, Cu, Si, and Al
atoms suspended between semi-infinite Co leads. We employ the screened
Korringa-Kohn-Rostoker Green's function method for the electronic structure
calculation and evaluate the conductance in the ballistic limit using the
Landauer approach. The conductance through the constrictions reflects the
spin-splitting of the Co bands and causes high MR ratios, up to 50%. The
influence of the structural changes on the conductance is studied by
considering different geometrical arrangements of atoms forming the chains. Our
results show that the conductance through s-like states is robust against
geometrical changes, whereas the transmission is strongly influenced by the
atomic arrangement if p or d states contribute to the current.Comment: Revised version, presentation of results is improved, figure 2 is
splitted to two figure
Exploring the nexus between banking sector reform and performance: Evidence from newly acceded EU countries
Exploring the nexus between banking sector reform and performance: Evidence from newly acceded EU countriesnexus, banking sector, banking sector, EU countries
Ballistic Spin Injection from Fe into ZnSe and GaAs with a (001), (111), and (110) orientation
We present first-principles calculations of ballistic spin injection in
Fe/GaAs and Fe/ZnSe junctions with orientation (001), (111), and (110). We find
that the symmetry mismatch of the Fe minority-spin states with the
semiconductor conduction states can lead to extremely high spin polarization of
the current through the (001) interface for hot and thermal injection
processes. Such a symmetry mismatch does not exist for the (111) and (110)
interfaces, where smaller spin injection efficiencies are found. The presence
of interface states is found to lower the current spin polarization, both with
and without a Schottky barrier. Finally, a higher bias can also affect the spin
injection efficiency.Comment: 12 pages, 18 figure
Broken-Bond Rule for the Surface Energies of Noble Metals
Using two different full-potential ab-initio techniques we introduce a
simple, universal rule based on the number of broken first-neighbor bonds to
determine the surface energies of the three noble metals Cu, Ag and Au. When a
bond is broken, the rearrangement of the electronic charge for these metals
does not lead to a change of the remaining bonds. Thus the energy needed to
break a bond is independent of the surface orientation. This novel finding can
lead to the development of simple models to describe the energetics of a
surface like step and kink formation, crystal growth, alloy formation,
equilibrium shape of mesoscopic crystallites and surface faceting.Comment: 4 pages, 2 figure
Coordination Dependence of Hyperfine Fields of 5sp Impurities on Ni Surfaces
We present first-principles calculations of the magnetic hyperfine fields H
of 5sp impurities on the (001), (111), and (110) surfaces of Ni. We examine the
dependence of H on the coordination number by placing the impurity in the
surfaces, on top of them at the adatom positions, and in the bulk. We find a
strong coordination dependence of H, different and characteristic for each
impurity. The behavior is explained in terms of the on-site s-p hybridization
as the symmetry is reduced at the surface. Our results are in agreement with
recent experimental findings.Comment: 4 pages, 3 figure
Monte Carlo simulations of ferromagnetism in p-CdMnTe quantum wells
Monte Carlo simulations, in which the Schrodinger equation is solved at each
Monte Carlo sweep, are employed to assess the influence of magnetization
fluctuations,short-range antiferromagnetic interactions, disorder, magnetic
polaron formation, and spin-Peierls instability on the carrier-mediated Ising
ferromagnetism in two-dimensional electronic systems. The determined critical
temperature and hysteresis are affected in a nontrivial way by the
antiferromagnetic interactions. The findings explain striking experimental
results for modulation-doped p-CdMnTe quantum wells.Comment: 4 pages, 4 figures, to be published in Physical Review Letters;
replaced figure 4; revised tex
Lung cryobiopsy for the diagnosis of interstitial lung diseases: A series contribution to a debated procedure
Introduction: Transbronchial cryobiopsy is an alternative to surgical biopsy for the diagnosis of fibrosing interstitial lung diseases, although the role of this relatively new method is rather controversial. Aim of this study is to evaluate the diagnostic performance and the safety of transbronchial cryobiopsy in patients with fibrosing interstitial lung disease. Materials and methods: The population in this study included patients with interstitial lung diseases who underwent cryobiopsy from May 2015 to May 2018 at the Division of Pneumology of San Giuseppe Hospital in Milan and who were retrospectively studied. All cryobiopsy procedures were performed under fluoroscopic guidance using a flexible video bronchoscope and an endobronchial blocking system in the operating room with patients under general anaesthesia. The diagnostic performance and safety of the procedure were assessed. The main complications evaluated were endobronchial bleeding and pneumothorax. All cases were studied with a multidisciplinary approach, before and after cryobiopsy. Results: Seventy-three patients were admitted to this study. A specific diagnosis was reached in 64 cases, with a diagnostic sensitivity of 88%; 5 cases (7%) were considered inadequate, 4 cases (5%) were found to be non-diagnostic. Only one major bleeding event occurred (1.4%), while 14 patients (19%) experienced mild/moderate bleeding events while undergoing bronchoscopy; 8 cases of pneumothorax (10.9%) were reported, of which 2 (2.7%) required surgical drainage. Conclusions: When performed under safe conditions and in an experienced center, cryobiopsy is a procedure with limited complications having a high diagnostic yield in fibrotic interstitial lung disease
Origin of the giant magnetic moments of Fe impurities on and in Cs films
To explore the origin of the observed giant magnetic moments ()
of Fe impurities on the surface and in the bulk of Cs films, we have performed
the relativistic LSDA + U calculations using the linearized muffin-tin orbital
(LMTO) band method. We have found that Fe impurities in Cs behave differently
from those in noble metals or in Pd. Whereas the induced spin polarization of
Cs atoms is negligible, the Fe ion itself is found to be the source of the
giant magnetic moment. The 3d electrons of Fe in Cs are localized as the 4f
electrons in rare-earth ions so that the orbital magnetic moment becomes as
large as the spin magnetic moment. The calculated total magnetic moment of , which comes mainly from Fe ion, is close to the experimentally
observed value.Comment: 4 pages including 3 figures and 1 table. Submitted to PR
Towards New Half-Metallic Systems: Zinc-Blende Compounds of Transition Elements with N, P, As, Sb, S, Se, and Te
We report systematic first-principles calculations for ordered zinc-blende
compounds of the transition metal elements V, Cr, Mn with the sp elements N, P,
As, Sb, S, Se, Te, motivated by recent fabrication of zinc-blende CrAs, CrSb,
and MnAs. They show ferromagnetic half-metallic behavior for a wide range of
lattice constants. We discuss the origin and trends of half-metallicity,
present the calculated equilibrium lattice constants, and examine the
half-metallic behavior of their transition element terminated (001) surfaces.Comment: 2nd Version: lattice constants calculations added, text revise
Surface Properties of the Half- and Full-Heusler Alloys
Using a full-potential \textit{ab-initio} technique I study the electronic
and magnetic properties of the (001) surfaces of the half-Heusler alloys,
NiMnSb, CoMnSb and PtMnSb and of the full-Heusler alloys CoMnGe, CoMnSi
and CoCrAl. The MnSb terminated surfaces of the half-Heusler compounds
present properties similar to the bulk compounds and, although the
half-metallicity is lost, an important spin-polarisation at the Fermi level. In
contrast to this the Ni terminated surface shows an almost zero net
spin-polarisation. While the bulk CoMnGe and CoMnSi are almost
half-ferromagnetic, their surfaces lose the half-metallic character and the net
spin-polarisation at the Fermi level is close to zero. Contrary to these
compounds the CrAl terminated (001) surface of CoCrAl shows a spin
polarisation of about 84%.Comment: 14 pages, 6 figure
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