1,721,018 research outputs found
Role of geometrical symmetry in thermally activated processes in clusters of interacting dipolar moments
No full textThermally activated magnetization decay is studied in ensembles of clusters of interacting dipolar moments by applying the master-equation formalism, as a model of thermal relaxation in systems of interacting single-domain ferromagnetic particles. Solving the associated master equation reveals a breakdown of the energy barrier picture depending on the geometrical symmetry of structures. Deviations are most pronounced for reduced symmetry and result in a strong interaction dependence of relaxation rates on the memory of system initialization. A simple two-state system description of an ensemble of clusters is developed, which accounts for the observed anomalies. These results follow from a semianalytical treatment, and are fully supported by kinetic Monte Carlo simulations
Consistent energy barrier distributions in magnetic particle chains
No full textWe investigate long-time thermal activation behaviour in magnetic particle chains of variable length. Chains are modelled as Stoner–Wohlfarth particles coupled by dipolar interactions. Thermal activation is described as a hopping process over a multidimensional energy landscape using the discrete orientation model limit of the Landau–Lifshitz–Gilbert dynamics. The underlying master equation is solved by diagonalising the associated transition matrix, which allows the evaluation of distributions of time scales of intrinsic thermal activation modes and their energy representation. It is shown that as a result of the interaction dependence of these distributions, increasing the particle chain length can lead to acceleration or deceleration of the overall relaxation process depending on the initialisation procedure
Distribution of switching fields in magnetic granular materials
No full textWe present analytical calculations and kinetic Monte-Carlo modeling of rate-dependent behavior of switching field distributions (SFDs) in an ensemble of Stoner-Wohfarth particles, assuming distributions of anisotropies and volumes, and thermal activation included by the Néel-Brown theory. By applying probabilistic arguments, we show that the SFD can be self-consistently separated into the contribution from distributions of intrinsic properties of particles and the (irreducible) contribution resulting solely from thermal fluctuations, which is shown to become a significant effect at sweep rates relevant to the recording process. This provides a unifying framework for systematic analysis of different classes of system
Atomistic calculation of the thickness and temperature dependence of exchange coupling through a dilute magnetic oxide
No full textThe exchange coupling of two magnetic layers via a diffuse oxide interlayer is studied with an atomistic spin model. We investigate the effect of magnetic concentration and oxide layer thickness on the effective exchange coupling strength and find an exponential dependence of the coupling strength on the oxide thickness without the need for magnetic pinholes. Furthermore we show that exchange coupling has a strong temperature dependence which is significant for the reversal dynamics during heat assisted magnetic recording
Interaction effects enhancing magnetic particle detection based on magneto-relaxometry
No full textWe investigated the effects of dipolar interactions on the long-time magnetization decay M(t) in clusters of magnetic nanoparticles. Applying the Néel-Arrhenius thermal activation picture shows that M(t) generally follows stretched exponential behavior, dependent not only on the dipolar interaction strength, geometry of particle arrangement within clusters, but also on the field history applied during the initialization. As demonstrated, combining these factors could serve to enhance the degree of resolution in magnetic particle detection based on magneto-relaxometry
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
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