1,721,096 research outputs found
Magnetization reversal via single and double vortex states in submicron Permalloy ellipses
No full textThe magnetization reversal mechanism in an array of submicron elliptical Permalloy elements with an aspect ratio 1.4:1 is investigated using the diffracted magneto-optic Kerr effect technique, Lorentz scanning transmission electron microscopy, and Lorentz transmission electron microscopy. The experimental results are interpreted from a comparison with micromagnetic simulations. The reversal mechanism is found to be dependent on the direction of the magnetic field and to occur via the formation of one or two vortices; the one vortex state is nucleated when the field is applied along the short axis. For the field applied along the long axis a mixture of one- and two-vortex states is observed at remanence
Magnetization switching in Permalloy square ring magnets
No full textThe magnetization switching in Permalloy square rings was studied using diffraction magneto-optic Kerr effect combined with numerical micromagnetic simulations. A two-step switching process was shown as the external field was swept along both the ring edge and the diagonal. Results showed that in order to reproduce the observed two-step reversal, slight asymmetry has to be introduced into the ring shape
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
Vortex chirality in an array of ferromagnetic dots
No full textMagnetization of an array of submicron permalloy dots was investigated using the diffracted magneto-optical Kerr effect. The shapes of the higher-order hysteresis loops are explained by the magnetic form factors associated with a vortex spin structure in each disk. The imaginary part of the form factor also explains the unexpected measured differences between hysteresis loops obtained on positive and negative diffraction orders. Shape effects account for the coherent chirality of the vortices over the arra
Spin excitations of magnetic vortices in ferromagnetic nanodots
No full text---Spin excitations of the magnetic vortex state in ferromagnetic nanodots are measured using Brillouin light scattering. Arrays of permalloy dots with 800-nm diameter and 60-nm thickness were fabricated by means of electron beam lithography and lift-off procedures. Two excitation modes are observed experimentally in the vortex state. One mode, at ∼12 GHz, decreases slightly in frequency to 11 GHz as an in-plane magnetic field is applied. The lower mode, at ∼8 GHz, is almost independent of applied field strength. Numerical and analytical calculations of the dynamic magnetization based on the Landau-Lifshitz equation of motion allows us to identify the higher and lower frequency modes as corresponding to dipole-dominated spin excitations localized inside the dot and at the dot edges, respectively
Metastable states during magnetization reversal in square permalloy rings
No full textThe magnetic reversal process in a two-dimensional array of permalloy square rings is presented. Rings of thickness of 25 nm, of lateral size of 2.1 μm, and with ring width of 240 nm were microfabricated using electron-beam lithography and lift-off techniques. Analysis of the diffracted magneto-optical Kerr effect hysteresis loops, magnetic force microscopy images, and micromagnetic simulations show that the magnetization reversal path depends on the direction of the in-plane applied magnetic field. On reducing the field from saturation, for fields along an edge or a diagonal of the square, the “onion” state is the stable state at remanence. In a narrow field range around reversal we find that the reversal occurs via a metastable intermediate state. For fields along the diagonal this intermediate state is a magnetic vortex. When the field is applied along an edge direction the intermediate state is a “horseshoe” state
Formation of stripe domains in Cobalt bars via a magnetic soft mode instability
No full textWe theoretically study the relation between stripe domains at remanence and magnetic normal modes in a single crystal Co bar. We find different stripe patterns depending on field history and in each case the domain structure can be related to a soft mode that triggers a phase transition. The stripe domain structure when the external field is along the long axis of the bar is shown to be generated by a standing wave mode, which has the same spatial structure as the stripes. At all fields this mode has the lowest frequency of all the standing wave modes. This mode goes soft at a second-order phase transition where the stripe domains emerge. For other directions of the field, the symmetry of soft modes is found to be consistent with the change in symmetry of the ground state and that the phase transition can be first order. An analytical model relating phase transitions and soft mode behavior is also briefly discussed
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