1,721,044 research outputs found
Micromagnetic Study of Electrical-Field-Assisted Magnetization Switching in MTJ Devices
No full textPerpendicular MgO-based magnetic tunnel junctions are optimal candidates as building blocks of spin-transfer torque (STT) magnetoresistive memories. However, up to now, the only STT is not enough to achieve switching current density below A/cm . A recent work has experimentally demonstrated the possibility of performing magnetization switching assisted by an electric-field at ultralow current density. Theoretically, this switching has been studied using a macrospin approach only. Here, we show a full micromagnetic study. We found that the switching occurs via a complex nucleation process including the nucleation of magnetic vortexes
Skyrmion motion induced by spin-Hall current in constrained geometries
No full textMagnetic skyrmions are topologically protected spin textures typical of chiral magnets characterized
by a special kind of exchange interaction known as Dzyaloshinkii-Moriya interaction (DMI).
In the last years growing interest has been addressed to the study of these topological defects both
from a fundamental point of view and for its several technological applications like for instance
their usage as information carriers [1]. Great attention has been also given to skyrmion nucleation,
stability and motion in confined magnetic systems under the influence of a spin-current [2,3].
Recently, the effect of confinement has been studied in the presence of spin-polarized current [2],
but there are not yet studies focusing on the skyrmion motion driven by SHE in constrained
geometries.
Here, we solve analytically Thiele’s equation in the presence of spin-Hall effect (SHE) with no
external field and by taking into account confinement. The spin-Hall current injected in the heavy
metal along the x direction (see Fig.1 (a)) combined with the interfacial DMI favors the Néel skyrmion
(hedgehog-like) nucleation in a thin magnetized stripe. We model confinement effects by
introducing a potential V(r) which arises at the boundaries of the magnetic stripe. This potential can
be thought of as a positive barrier having a repulsive nature associated to the static magnetization
rotation at the stripe borders. The Nèel skyrmions is interpreted as a quasi-particle which interacts
repulsively with this barrier. As a result, its trajectory is deviated
Topological skyrmion dynamics driven by spin-transfer torque
No full textVery recently, an important class of magnetic solitons called magnetic skyrmions has been widely
studied [1,2]. The stability of these topological defects has been analyzed in the presence of intrinsic
dissipation both as a function of Dzyaloshinskii–Moriya interaction (DMI) and as a function of
a spin-polarized current (SPC).
Here, we show that in a spin-valve consisting of Pt(5 nm)/Co(0.6 nm)/Cu (4 nm)/CoPt(4 nm) a
perpendicular spin current, in the presence of the DMI [3,4] and strong perpendicular anisotropy,
induces the rotation of the spins from the hedgehog-like to the vortex-like texture in the topological
droplet state and excites low-frequency topological modes. The SPC is injected locally in the Co
giving rise to the local excitation of the magnetization. The Pt heavy metal adds a further degree of
freedom, the interfacial DMI, to the effective field of the Co. The FL has a square cross section of
400 x 400 nm2, while the point contact has a diameter of 70 nm. Both FL and polarizer have out-ofplane
magnetic state at zero bias field. The “topological droplet” state (integer skyrmion number)
arises and its dynamical response, namely a “topological mode” (TM), can be excited and sustained
by a SPC. The low-frequency TM is linked to a continual conversion from hedgehog-like (Néel
skyrmion) to vortex-like (Bloch skyrmion) state, preserving the topology represented by the skyrmion
number S = -1. A negative current (J < 0) flows from the free layer (Co) to the fixed (nanocontact,
CoPt) layer. The topological character of these spin-wave excitations results from the
synchronized dynamics between the 360o rotation of the spin of the outer droplet domain and the
expansion/shrinking of the droplet core.
A quantitative description of topological droplet modes is given according to an analytical model
based on the linearization of the equations of motion including intrinsic positive Gilbert damping
and negative damping related to the spin-transfer torque. The analytical frequency of the topological
droplet mode is expressed as the solution of a second-order algebraic equation written in terms
of the magnetic parameters including the intrinsic and extrinsic damping
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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