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 $\mu_B$. 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 Ti1−x_{1-x}Cox_{x}O_{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 $p$-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 $J$ (or equivalently $U$). The ferromagnetic transition temperature $T_c$, deteremined within the spin-fluctuation theory, corresponds closely with the observed $T_c$ 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 $2 \times 9$. While the substitution of the transition metal atoms may preserve the half-ferromagnetic character, substituting the $sp$ 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