1,721,103 research outputs found
X-ray structural investigation of Co∕Cu granular multilayers with giant magnetoresistance
No full textMagnetic nanogranular materials, viz. systems made of nanosized magnetic (M) particles dispersed in a non magnetic (NM) matrix, belong to a class of materials that show an enhanced magnetoresistive effect, the so called giant magnetoresistance (GMR). In particular, in nanogranular systems the M/NM interface area is high and so the spin-dependent scattering that originates GMR is promoted. GMR intensity and efficiency are related to the magnetic and structural properties of the granular samples, and in this paper we focus on this latter topic. More in detail we study how the structural features, the growth process and, along with that, interfacial roughness, are related to nanoparticle size.
In this paper, we concentrate on samples produced combining the typical multilayer stacking with the presence of very thin M layers [1]. Actually, below a critical thickness a layer fragmentation process is induced and a granular arrangement of the magnetic species is obtained. We investigated Co/Cu fragmented multilayers, and we followed the structure and interfacial roughness evolution as the thickness of the Co layers is reduced, viz. changing M particles average size. This was possible as, thanks to the inner vertical periodicity of the samples, we used structural techniques such as X-Ray specular reflectivity and grazing incidence small angle X-Ray (GISAXS) scattering to probe the vertical arrangement of the nanograins and the self- and cross-correlation of M/NM interfaces. Due to the small difference between Co and Cu electronic density, the measurements were performed in anomalous conditions, i.e. tuning X-Ray energy in order to enhance the otherwise poor optical contrast. The nanocrystalline structure of the samples was investigated with diffraction measurements, performed both in grazing incidence as well as in the usual theta-2theta configuration; details about the way in which the growth process of the granular multilayers develops and influences samples structure were accessed, as well, since GISAXS patterns reflect the universality class which the growth process belongs to [2]. The findings deduced from the X-Ray analysis will be presented and compared with the magnetic and magnetoresistive properties of the granular samples.
[1] G. Turilli, L. Pareti, and L. Castaldi, Superlattices and microstructures 25, 591 (1999). F. Casoli et al., J. Magn. Magn. Mat. 262/1, 69 (2003).
[2] R. Paniago et al., Phys. Rev. B 56(20) 13442 (1997)
(+)-Laburnamine, a natural selective ligand and partial agonist for the α4β2 nicotinic receptor subtype
No full textInterplay between spontaneous in‐plane long range order and vertical correlation length in sputtered Co/Cu multilayers
No full textThe interplay between non--local phenomena during growth and the evolution of interfacial roughness was investigated in Co/Cu multilayers grown by rf-magnetron sputtering. In particular, we compared samples where the presence of correlated interfacial roughness, namely interface undulations, is more or less pronounced by changing the underlayer or the multilayer stacking. We performed anomalous grazing incidence measurements to observe how the vertical correlation length, x_perp, changes as a function of the in-plane length scale of the roughness, L. x_perp is expected to monotonically decrease with L, but we found that x_perp displays a maximum for specific L values featuring a high degree of in-plane correlation. This effect seems to be related with the features of the multilayer stacking
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
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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe 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
Synthesis of nanostructured magnetic photocatalyst by colloidal approach and spray–drying technique
No full textNanostructured particles with a magnetic core and a photocatalytic shell are very interesting systems for
their properties to be magnetically separable (and so reusable) in photocatalytic water depuration
implant. Here, a robust, low time-consuming, easily scale up method to produce Fe3O4/SiO2/TiO2 hierarchical
nanostructures starting from commercial precursors (i.e. Fe3O4, SiO2) by employing a colloidal
approach (i.e. heterocoagulation) coupled with the spray–drying technique is presented. In particular,
a self-assembled layer-by-layer methodology based on the coagulation of dissimilar colloidal particles
was applied. First, a passive layer of silica (SiO2, amorphous) was created on magnetite in order to avoid
detrimental phenomena arising from the direct contact between magnetite and titania, then the deposition
of titania onto silica-coated-magnetite was promoted. TiO2, SiO2 and Fe3O4 nanosols were characterized
in terms of zeta potential, optimized and a self-assembled layer-by-layer approach was followed in
order to promote the heterocoagulation of silica onto magnetite surface and of titania onto silica coated
magnetite. Once optimized the colloidal route, the mixture was then spray-dried to obtain a granulated
powder with nano-scale reactivity, easier to handle and re-disperse in comparison to starting nanopowders
with the same surface properties. The nanostructured particles have been characterized by different
techniques such as SEM, TEM, XDR and their magnetic properties have been investigated. Moreover, preliminary
photocatalytic texts have been performed
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