1,721,024 research outputs found
Giant spin-dependent Seebeck effect from fully spin-polarized carriers in n-doped EuTiO3: a prototype material for spin-caloritronic applications
No full textSpin-caloritronics, the generation of spin currents and spin voltages from an applied temperature gradient, is a visionary technology with outstanding potential for novel applications and a fascinating landscape of fundamental properties. These capabilities have been revealed so far in a variety of devices typically assembled as interfaces between magnetic and non-magnetic materials. Here, using advanced ab initio calculations, we provide evidence that giant effects can be obtained in the electron-doped bulk oxide EuTiO3. We find this material to be a half-metal, 100% spin-polarized ferromagnet for a wide range of temperatures and carrier concentrations. The combination of high electron mobility, a large Seebeck coefficient, and full spin polarization realizes the perfect conditions to achieve giant spin-polarized thermopower and huge chemical potential imbalance between the spin channels. At low temperatures, our calculations predict spin current densities similar to 0.1 mA cm(-2) per unitary temperature gradient, and spin voltages of mV K-1 order, which are among the highest reported so far. In addition, our analysis lays down fundamental guidelines for the design of the best suited materials for spin-caloritronic applications
Fundamentals of NaMnO2, the cathode material for Na-ion rechargeable batteries
No full textSodium manganese oxide (NaMnO2) is perhaps the most promising cathode material for Na-ion rechargeable batteries, owing to a reported charge capacity comparable to that of commercial LiCoO2. The combination of earth abundant and environmentally benign atomic constituents and the good thermodynamic and structural stability makes NaMnO2 a potential cornerstone for Li-ion replacement in batteries. At the fundamental level, NaMnO2 is characterized by a complex landscape of intertwined structural, electronic, and magnetic properties. Using a combination of advanced ab initio approaches, we reveal a nature far more intriguing than typically reported. Strikingly, while magnetic frustration is commonly believed to dominate the behavior of both α and β polymorphs, we find its impact largely suppressed due to the formation of MnO2 stripes patterned by a peculiar magnetic ordering at the intra-atomic length scale. This phenomenon underlies the extremely anisotropic magnetic interactions and establishes NaMnO2 as a paradigmatic case of magnetic frustration primarily relieved by electronic mechanisms, rather than by structural distortions
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Variations on the Author
Get PDF“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
Get PDFWe 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
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
A promising outlook on the development of lead halide perovskites as spin-orbitronic materials
Get PDFHybrid lead halide perovskites have progressively overcome the horizon of materials for novel, highly efficient solar cells and are now proposed for a variety of optoelectronic, nanoelectronic, and thermoelectric applications. In this Perspective, we focus on a still scarcely explored and yet extremely thrilling playground: the use of lead halide perovskites to design efficient magneto-electronic and magneto-optic applications. Our analysis is pointed to emphasize the unique combination of strong spin-orbit coupling and wide structural and chemical flexibility, which characterize the lead halide perovskites. Using model calculations, we furnish a qualitative evidence of their capabilities for what concerns the charge-spin conversion mechanism, which is basic to some of the most visionary spin-orbitronic implementations, such as the magnetoelectric switching and the spin-diffusive transisto
Fermi Surface Topology and Rashba‐Edelstein Charge‐Spin Conversion in Lead‐Halide Perovskites
Get PDFThe conversion of charge current into spin current by the Rashba-Edelstein effect enables the reciprocal control of electron charge and magnetization in magnetoelectric and magneto-optical devices. The fundamentals of this effect are described in 3D lead-halide perovskites: due to spin-momentum locking, a strong charge-spin conversion, widely tunable by the injected charge density, is envisaged. The analysis highlights the close relationship between charge-spin conversion and the topological transition occurring from the low-density, torus-shaped Fermi surface (genus 1) to the high-density, simply connected Fermi surfaces (genus 0). At room temperature, spin-polarizations as large as approximate to 10% are obtained for input charge currents in the approximate to 102 to 106 Acm(-2) range; at low temperature, almost full spin-polarization can be achieved, owed to the large, impurity scattering-limited mobilities. The results qualify lead-halide perovskites as suitable materials for spin-orbitronic applications
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