628 research outputs found
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
Community-level Distribution of Misoprostol to Prevent Postpartum Hemorrhage at Home Births in Northern Nigeria
In Nigeria, most deaths due to postpartum hemorrhage (PPH) occur in the absence of skilled birth attendants. A study using community mobilization and the training of community drug keepers to increase access to misoprostol for PPH prevention was conducted in five communities around Zaria in Kaduna State, Nigeria. Community-oriented resource persons (CORPs) and traditional birth attendants (TBAs) recruited and counseled pregnant women on bleeding after delivery, the importance of delivery at a health facility, and the role of misoprostol. Drug keepers stored and dispensed misoprostol during a woman’s third trimester of pregnancy. TBAs and CORPs enrolled 1,875 women from January through December 2009. These results are based on 1,577 completed postpartum interviews. Almost all women delivered at home (95%) and skilled attendance at delivery was low (7%). The availability of misoprostol protected 83% of women who delivered at home against PPH who otherwise would not have been protected. Policymakers working in similar contexts should consider utilizing commuity-level distribution models to reach women with this life-saving intervention. Afr J Reprod Health 2014; 18[2]: 166-175).Keywords: misoprostol, community-level distribution, Nigeria, maternal mortality Au Nigeria, la plupart des décès dus à une hémorragie du post-partum (HPP) se produisent en l'absence d'accoucheuses qualifiées. Une étude à travers la mobilisation communautaire et la formation des gardiens de drogues dans la communauté pour améliorer l'accès à misoprostol pour la prévention de l'HPP a été menée dans cinq communautés à l’alentour de Zaria dans l'État de Kaduna, au Nigeria. Les experts orientés vers les communautés (EOVC) et les accoucheuses traditionnelles (AT) ont été recrutés et ont conseillés aux femmes enceintes sur les saignements après l'accouchement, l'importance de l’accouchement dans un établissement de santé, et le rôle de misoprostol. Les gardiens de médicaments ont stocké et distribué misoprostol au cours du troisième trimestre de la grossesse de la femme. Les et les accoucheuses traditionnelles et les EOVC ont inscrit 1875 femmes de janvier à décembre 2009. Ces résultats sont basés sur 1 577 entrevues post-partum déjà terminées. Presque toutes les femmes ont accouché à domicile (95%) et l'assistance à l’accouchement par le personnel qualifié était faible (7%). La disponibilité de misoprostol a protégé 83% des femmes qui ont accouché à domicile contre l’HPP qui, autrement, n'auraient pas été protégées. Les décideurs qui travaillent dans des contextes similaires devraient envisager d'utiliser des modèles de distribution au niveau de la communauté pour atteindre les femmes à travers cette intervention de sauvetage. Afr J Reprod Health 2014; 18[2]: 166-175).Mots clés: misoprostol, distribution au niveau de la communauté, Nigeria, mortalité maternelle
Surface Half-Metallicity of CrAs in the Zinc-Blende Structure
The development of new techniques such as the molecular beam epitaxy have
enabled the growth of thin films of materials presenting novel properties.
Recently it was made possible to grow a CrAs thin-film in the zinc-blende
structure. In this contribution, the full-potential screened KKR method is used
to study the electronic and magnetic properties of bulk CrAs in this novel
phase as well as the Cr and As terminated (001) surfaces. Bulk CrAs is found to
be half-ferromagnetic for all three GaAs, AlAs and InAs experimental lattice
constants with a total spin magnetic moment of 3 . The Cr-terminated
surface retains the half-ferromagnetic character of the bulk, while in the case
of the As-termination the surface states destroy the gap in the minority-spin
band.Comment: 4 pages, 2 figures, new text, new titl
Ferromagnetism in laser deposited anatase TiCoO_{2-\delta} films
Pulsed laser deposited films of Co doped anatase TiO2 are examined for Co
substitutionality, ferromagnetism, transport, magnetotransport and optical
properties. Our results show limited solubility (up to ~ 2 %) of Co in the
as-grown films and formation of Co clusters thereafter. For Ti0.93Co0.07O2-d
sample, which exhibits a Curie temperature (Tc) over 1180 K, we find the
presence of 20-50 nm Co clusters as well as a small concentration of Co
incorporated into the remaining matrix. After being subjected to the high
temperature anneal during the first magnetization measurement, the very same
sample shows a Tc ~ 650 K and almost full matrix incorporation of Co. This Tc
is close to that of as-grown Ti0.99Co0.01O2-d sample (~ 700 K). The transport,
magnetotransport and optical studies also reveal interesting effects of the
matrix incorporation of Co. These results are indicative of an intrinsic
Ti1-xCoxO2-d diluted magnetic semiconductor with Tc of about 650-700 K.Comment: 14 pages + 9 figure
The effect of the spin-orbit interaction on the band gap of half-metals
The spin-orbit interaction can cause a nonvanishing density of states (DOS)
within the minority-spin band gap of half-metals around the Fermi level. We
examine the magnitude of the effect in Heusler alloys, zinc-blende half metals
and diluted magnetic semiconductors, using first-principles calculations. We
find that the ratio of spin-down to spin-up DOS at the Fermi level can range
from below 1% (e.g. 0.5% for NiMnSb) over several percents (4.2% for (Ga,Mn)As)
to 13% for MnBi.Comment: 5 pages, 3 figure
A search for ferromagnetism in transition-metal-doped piezoelectric ZnO
We present the results of a computational study of ZnO in the presence of Co
and Mn substitutional impurities. The goal of our work is to identify potential
ferromagnetic ground states within the (Zn,Co)O or (Zn,Mn)O material systems
that are also good candidates for piezoelectricity. We find that, in contrast
to previous results, robust ferromagnetism is not obtained by substitution of
Co or Mn on the Zn site, unless additional carriers (holes) are also
incorporated. We propose a practical scheme for achieving such -type doping
in ZnO
Ferromagnetism in a dilute magnetic semiconductor -- Generalized RKKY interaction and spin-wave excitations
Carrier-mediated ferromagnetism in a dilute magnetic semiconductor has been
studied using i) a single-impurity based generalized RKKY approach which goes
beyond linear response theory, and ii) a mean-field-plus-spin-fluctuation
(MF+SF) approach within a (purely fermionic) Hubbard-model representation of
the magnetic impurities, which incorporates dynamical effects associated with
finite frequency spin correlations in the ordered state. Due to a competition
between the magnitude of the carrier spin polarization and its oscillation
length scale, the ferromagnetic spin coupling is found to be optimized with
respect to both hole doping concentration and impurity-carrier spin coupling
energy (or equivalently ). The ferromagnetic transition temperature
, deteremined within the spin-fluctuation theory, corresponds closely with
the observed values. Positional disorder of magnetic impurities causes
significant stiffening of the high-energy magnon modes. We also explicitly
study the stability/instability of the mean-field ferromagnetic state, which
highlights the role of competing AF interactions causing spin twisting and
noncollinear ferromagnetic ordering.Comment: 10 pages, 12 figure
Origin and Properties of the Gap in the Half-Ferromagnetic Heusler Alloys
We study the origin of the gap and the role of chemical composition in the
half-ferromagnetic Heusler alloys using the full-potential screened KKR method.
In the paramagnetic phase the C1_b compounds, like NiMnSb, present a gap.
Systems with 18 valence electrons, Z_t, per unit cell, like CoTiSb, are
semiconductors, but when Z_t > 18 antibonding states are also populated, thus
the paramagnetic phase becomes unstable and the half-ferromagnetic one is
stabilized. The minority occupied bands accommodate a total of nine electrons
and the total magnetic moment per unit cell in mu_B is just the difference
between Z_t and . While the substitution of the transition metal
atoms may preserve the half-ferromagnetic character, substituting the atom
results in a practically rigid shift of the bands and the loss of
half-metallicity. Finally we show that expanding or contracting the lattice
parameter by 2% preserves the minority-spin gap.Comment: 11 pages, 7 figures New figures, revised tex
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