1,721,067 research outputs found
Interface magnetism and magnetic structure of GdN∕Fe multilayers studied by x-ray magnetic circular dichroism
No full textWe have used the element specificity of x-ray magnetic circular dichroism to separate the contributions of the component layers to the magnetization and local magnetic structure of artificial nanoscale ferrimagnetic multilayers GdN/Fe. The Fe layers, by strong antiferromagnetic interlayer exchange coupling, not only magnetize a narrow interface region in paramagnetic GdN but induce long-range magnetic order in the volume of the GdN layers at temperatures considerably above the Curie temperature of the bare layers (T-C(GdN) approximate to 60 K), in support of a theoretical mean- field prediction. We propose that the effect may be related to the special electronic band structure of GdN, which shows a transition from narrow-gap semiconducting to metallic conduction at T-C(GdN). In an elevated external magnetic field the GdN- and Fe-sublayer magnetic moments adopt a canted configuration. In this state the local magnetization in each GdN layer is highly nonuniform at low temperature. The interior turns its moment into the field direction almost abruptly from one atomic layer to the next in a single block. This indicates weak magnetic coupling between the interfacial and volume magnetizations in GdN. The results are at variance with the much studied "model" multilayer system Gd/Fe, where magnetic order in the Gd-layer volume appears intrinsically only significantly below the Curie temperature of bulk Gd. Furthermore, magnetization reversal in the Gd layers in a magnetic field occurs gradually on a considerably larger length scale, only if they are sufficiently thick. (c) 2006 American Institute of Physics
An Introduction to Differential EXAFS
No full textDifferential EXAFS (DiffEXAFS) is a novel technique for measuring atomic perturbations on a local scale that result from the modulation of a given sample property. Experiments conducted to date have revealed a sensitivity to such perturbations of the order of femtometres, two orders of magnitude more sensitive than is considered possible by conventional EXAFS techniques. Here, the concept behind DiffEXAFS is described, and experimental factors required to detect such a signal discussed
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Energy Dispersive X-Ray Absorption Spectroscopy: Beamline Results and Opportunities
No full textID24 is the energy dispersive beamline of the European Synchrotron Radiation Facility dedicated to X‐ray Absorption Spectroscopy (XAS). Since 2000, a complete refurbishment program has started, including source upgrade, mirrors replacement, polychromator optimization and detection improvements. These have made possible the development of new applications in a variety of different fields, ranging from the measurement of tiny atom displacements to time resolved techniques, from measurements under extreme conditions to micro‐XAS studies
Probing atomic displacements with thermal differential EXAFS
No full textDifferential extended X-ray absorption fine structure (DiffEXAFS) is a novel technique for the study of small atomic strains. Here the development of this technique to the measurement of thermally induced strain is presented. Thermal DiffEXAFS measurements have been performed on -Fe and SrF2, yielding = (11.6 0.4) 10-6 K-1 and (19 2) 10-6 K -1, respectively. These are in good agreement with accepted values, proving the viability of the technique. Analysis has revealed sensitivity to mean atomic displacements of 0.3 fm
Interplay of Chemical, Electronic, and Structural Effects in the Triple-Conducting BaFeO3-Ba(Zr,Y)O3 Solid Solution
Full text linkTriple-conducting oxides with mobile protons, oxygen vacancies, and holes are key functional materials for protonic ceramic fuel/electrolysis cells. We comprehensively investigate the Ba(Zr,Y,Fe)O3-delta perovskite solid solution series ranging from electrolyte to electrode-type materials depending on iron content. From thermogravimetry and impedance spectroscopy, the proton and oxygen vacancy concentrations as well as electronic and ionic conductivities are determined. X-ray spectroscopy (Fe K-edge XANES, O K-edge Raman scattering, Fe, Zr, Y K-edge EXAFS) elucidates the finer features of the electronic structure and local distortions. A low Fe content of <= 10% strongly decreases the degree of hydration, while comparably high Fe concentrations of >= 70% are required to obtain an electronic conductivity sufficient for an electrode material. The transport of ionic and electronic carriers is interrelated in a complex way and is closely linked to details of the electronic structure (strength of Fe-O hybridization) and geometrical distortions (Fe-O-Fe and Fe-O-(Zr,Y) buckling). As a result, an optimum combination of proton concentration and electronic conductivity is not obtained in the middle of the solid solution series but rather found for Fe-rich materials with 20-30% doping with oversized, redox-inactive cations. A similar behavior is also expected for related solid solutions between a large-band gap electrolyte and small-band gap redox-active perovskites
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispersive XAS on a High Brilliance Source: Highlights and Future Opportunities
No full textEnergy Dispersive X‐ray Absorption Spectroscopy is a now a well‐established method which has been applied to a broad range of applications. Ten years from the construction of beamline ID24 at the ESRF, the first dispersive XAS spectrometer using undulator radiation on a third generation source, we report an overview of recent results in very diverse fields of research, ranging from automotive catalysts to magnetism at extreme conditions. We also illustrate how pushing the instrument to its limits has opened new opportunities, such as an enhanced sensitivity to detection of tiny atomic displacements and the potential for micro‐probe redox and speciation imaging
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