1,720,966 research outputs found
In situ TEM analysis of resistive switching in manganite based thin-film heterostructures
No full textThe mechanism of the electric-pulse induced resistance change effect in Au/Pr0.65Ca0.35MnO3/SrTi0.99Nb0.01O3 thin-film samples is studied by means of in situ electrical stimulation inside a transmission electron microscope. A detailed equivalent-circuit model analysis of the measured current voltage characteristics provides crucial information for the proper interpretation of the microscopy results. The electrical transport data of the electron-transparent samples used for the in situ investigations is verified by comparison to measurements of unpatterned thin-film samples. We find comprehensive evidence for electrochemical oxygen vacancy migration affecting the potential barrier of the pn junction between Pr0.65Ca0.35MnO3 and SrTi0.99Nb0.01O3 as well as the resistance of the manganite bulk. The high-resistance state formation in the Pr0.65Ca0.35MnO3 bulk is frequently accompanied by structural transformations, namely detwinning and superstructure formation, most likely as the result of the joint impact of dynamic charge inhomogenities by oxygen vacancy migration and injection of high carrier densities at the electrodes.Deutsche Forschungsgemeinschaft (DFG) [JO 348/10-1, SFB1073
Polaron absorption for photovoltaic energy conversion in a manganite-titanate pn heterojunction
No full textThe relation among structure, electric transport, and photovoltaic effect is investigated for a pn heterojunction with strong correlation interactions. A perovskite interface is chosen as a model system consisting of the p-doped strongly correlated manganite Pr0.64Ca0.36MnO3 (PCMO) and the n-doped titanate SrTi1-yNbyO3 (y = 0.002 and 0.01). High-resolution electron microscopy and spectroscopy reveal a nearly dislocation-free, epitaxial interface and give insight into the local atomic and electronic structure. The presence of a photovoltaic effect under visible light at room temperature suggests the existence of mobile excited polarons within the band-gap-free PCMO absorber. The temperature-dependent rectifying current-voltage characteristics prove to be mainly determined by the presence of an interfacial energy spike in the conduction band and are affected by the colossal electroresistance effect. From the comparison of photocurrents and spatiotemporal distributions of photogenerated carriers (deduced from optical absorption spectroscopy), we discuss the range of the excited polaron diffusion length
Nanocomposite stability in Fe-, Co-, and Mn-based perovskite/spinel systems
No full textFabrication of thin film nanocomposites via decomposition and self-assembly from the vapor phase is a promising path for cost-effective fabrication of multifunctional materials. In particular, oxides as a new class of energy materials allow for rich functionalities, e. g., by combining p-and n-doped systems in catalytic or light harvesting units. Combining A-site doped perovskites ABO(3) with CoFe2O4 spinel, we have investigated thin film phase composition and nanocomposite morphology in the pseudobinary system La0.6Sr0.4BO3-CoFe2O4 for B = Fe, Co, and Mn. We observe formation of an epitaxial two-phase nanocomposite for B = Fe, i.e., the coexistence of La0.6Sr0.4FeO3 and CoFe2O4. In contrast, for B = Co or Mn nanocomposites are formed, where perovskite La0.6Sr0.4BO3 solid solutions coexists with Co-rich spinel and periclase phases. We derive conclusions for the preparation of perovskite-spinel nanocomposites with well-designed doping levels.Deutsche Forschungsgemeinschaft [JO 348/8, SFB 602
Ferromagnetism in Lightly Doped Pr1-xCaxMnO3 (x=0.023, 0.036) Nanoparticles Synthesized by Microwave Irradiation
No full textAlthough the magnetic phase diagrams of bulk and thin film samples of Pr1-xCaxMnO3 (x <= 0.5) are widely explored, few works have been published on the magnetic properties of nanoparticles, especially in the lightly, doped regime. In this paper, microwave irradiation was used to synthesize the Pr0.977Ca0.023MnO3 and Pr0.964Ca0.036MnO3 Manganite phases with Pnma space group in the form of anisotropic nanoparticles. The phase identification, structural characteristics, and formation of the nanostructures were analyzed by Rietveld analysis of the X-ray diffraction patterns, electron microscopy, and combining thermal analysis with infrared spectroscopy, respectively. Transport measurements on the annealed samples revealed the insulating nature, and electrical conduction occurs through thermally activated hopping of small polarons. The Mn-O-c-Mn tilt angles in the MnO6 octahedra show considerable flattening (160.9 degrees and 167.6 degrees for x = 0.023 and x = 0.036, respectively), possibly enhancing the electronic double exchange and promoting ferromagnetism. Ferromagnetic ordering of Mn spins was indeed observed below 109 K, and interestingly, the magnetic moment for x = 0.036 was 3.92 mu(B)/f.u. at 5 K, which is higher than the saturated Mn magnetic moment (3.8 mu(B)). The enhanced magnetization is attributed to ordering of the Pr spins.University Grants Commission (UGC), New Delhi; IISER Kolkat
Magnetostatic interaction mechanisms in a two-dimensional composite magnet
No full textThe magnetization structure and the mechanisms of magnetic interaction in an artificial two-phase magnet are analyzed with magnetic force microscopy and magnetooptics. A model system built up of arrays of hard magnetic CoPt squares (5 mu m edge length) embedded in a soft magnetic permalloy matrix is investigated. Special emphasis is put on the characterization of the matrix magnetization and on the interaction between the matrix and the CoPt squares. Different effects on different length scales are observed. At large distances to the hard magnetic dots, the magnetization of the matrix relaxes and is dominated by the characteristic pattern of an antidot array. The stability of this pattern with respect to magnetic fields and its dependence on the magnetic history of the system is analyzed. Nearby the dots, the magnetostatic coupling between the matrix and the CoPt induces a fine scale modulation of the magnetization of the matrix. At inter-dot distances up to 1 mu m, the dot matrix interaction is prevalent and the matrix contributes essentially to the dot-dot interaction. We have studied the characteristics of this modulation, particularly considering their decay length and the interaction transfer mediated by the modulation. (C) 2011 American Institute of Physics. [doi:10.1063/1.3626059
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
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