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Sign inversion of the high-field Hall slope in epitaxial La0.5Ca0.5MnO3 thin films
No full textMagnetic and electrical properties of thin epitaxial films of the manganite La1-xCaxMnO3 (xapproximate to0.5) grown by pulsed laser deposition were investigated. The x=0.5 composition corresponds to a half-filled e(g) band and is situated on the border between ferromagnetic-metallic and antiferromagnetic-insulating behavior at low temperatures. Both different types of electrical behaviors are observed in samples with similar deposition parameters. This duality may be attributed to phase separation and the occurrence of percolating paths. The insulating La0.5Ca0.5MnO3 samples become metalliclike when magnetic fields of several tesla are applied. Hereby, resistivity drops up to six orders of magnitude occur at 50 K and 12 T. Hall effect measurements on a sample with spontaneous insulator-metal transition show a sign inversion of the high-field Hall slope around 106 K
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
Orbital Ordering and the Cooperative Jahn–Teller Effect in Single Crystals of the Magnetic Perovskite La7/8Sr1/8MnO3
No full textIn the low-doped magnetic perovskite La7/8Sr1/8MnO3, a strong coupling exists between crystal structure and magnetic and electronic properties. At room temperature, the material is in a paramagnetic-semiconducting state, showing a dynamic Jahn–Teller (DJT) ordering of the Mn3+ ions. Below TJT=269 K however, the crystal goes into a cooperative Jahn–Teller (CJT) state, exhibiting antiferrodistorsive orbital ordering of the MnO6 octahedra. This leads to an increase in resistivity by a factor of 2 and to a drop of the paramagnetic susceptibility by about 20% [Physica B 155 (1989) 362; Phys. Rev. Lett. 71 (1993) 2331]. Around TC=188 K, a ferromagnetic transition occurs while the CJT effect becomes gradually weaker. Below TC the sample is metallic-like and shows a considerable colossal negative magnetoresistance (CMR) effect. Finally, the material goes into a charge-ordered, insulating state below TCO=147 K where the CJT effect completely vanishes.
When crossing the face boundary from the DJT to the CJT state, the resistivity shows a jump-like increase by a factor of roughly 2.15. This results from a frustration of the charge transport at the onset of orbital ordering By assuming that each Mn4+ ion is surrounded only by Mn3+ nearest-neighbors and by taking into account only charge transport along the principal axes, the square-diagonals and the cube-diagonals, we are able to calculate a jump-like increase by a factor of roughly 2.15. This results from a frustration of the charge transport at the onset of orbital ordering. By assuming that each Mn4+ ion is surrounded only by Mn3+ nearest-neighbors and by taking into account only charge transport along the principal axes, the square-diagonals and the cube-diagonals, we are able to calculate a jump ratio of 2.26, corresponding well to the experimental value. The CJT transition also causes a sudden decrease in the magnetic moment, which has been studied by performing field-dependent SQUID measurements around TJT. Since the crystal is in a paramagnetic state around TJT, the magnetization M scales with the Brillouin function β(J), where J is the spin of small ferromagnetic clusters. Fitting the magnetization data with the Brillouin function results in a CJT-induced shrinking of magnetic clusters from roughly four Mn ions to three Mn ions. These cluster sizes can also be understood in terms of the orbital structure of the material in both phases
Influence of the morphology on the magneto-transport properties of laser-ablated ultrathin La0.7Ba0.3MnO3 films
No full textDispelling 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
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