1,720,958 research outputs found
GdN thin films: Bulk and local electronic and magnetic properties
No full textA study of high-quality thin films of the ferromagnet gadolinium nitride, GdN, is reported. The films, prepared by reactive ion-beam sputtering, show good stoichiometry and the lattice parameter, Curie temperature T-C, and saturation magnetization of the bulk material. The electrical conductivity is thermally activated down to the onset of magnetic ordering where there is evidence of a transition to metallic behavior. The transition can be tuned by a magnetic field, as reflected by a giant negative magnetoresistance. The ordered 4f moment extracted from the spectra of x-ray magnetic circular dichroism at the gadolinium M-4,M-5 edges is consistent with the S-8(7/2) configuration of Gd3+; it varies with temperature as the macroscopic magnetization of the GdN layers. The experimental K-edge photoabsorption spectra of nitrogen in this compound indicate the presence of N p character of the low-lying unoccupied conduction-band states, pointing to hybridization of the N 2p and Gd (5d,6s) states. However, a comparison of the spectra with the theoretical partial density of vacant N p states shows considerable disparities that are not well understood. The exchange field generated by the Gd f electrons in the ferromagnetic phase of GdN induces a magnetic polarization of the N p band states, as can be concluded from the observation of strong magnetic circular dichroism at the K edge of nitrogen. It indicates the presence of an important spin-orbit interaction in the final N p states
Nanofabrication of spin-transfer torque devices by a polymethylmethacrylate mask one step process: Giant magnetoresistance versus single layer devices
No full textWe present a method to prepare magnetic spin torque devices of low specific resistance in a one step lithography process. The quality of the pillar devices is demonstrated for a standard magnetic double layer device. For single layer devices, we found hysteretic switching and a more complex dynamical excitation pattern in higher fields. A simple model to explain the resistance spikes is presented. (c) 2007 American Institute of Physics
Interface magnetism and magnetic structure of GdN∕Fe multilayers studied by x-ray magnetic circular dichroism
No full textWe have used the element specificity of x-ray magnetic circular dichroism to separate the contributions of the component layers to the magnetization and local magnetic structure of artificial nanoscale ferrimagnetic multilayers GdN/Fe. The Fe layers, by strong antiferromagnetic interlayer exchange coupling, not only magnetize a narrow interface region in paramagnetic GdN but induce long-range magnetic order in the volume of the GdN layers at temperatures considerably above the Curie temperature of the bare layers (T-C(GdN) approximate to 60 K), in support of a theoretical mean- field prediction. We propose that the effect may be related to the special electronic band structure of GdN, which shows a transition from narrow-gap semiconducting to metallic conduction at T-C(GdN). In an elevated external magnetic field the GdN- and Fe-sublayer magnetic moments adopt a canted configuration. In this state the local magnetization in each GdN layer is highly nonuniform at low temperature. The interior turns its moment into the field direction almost abruptly from one atomic layer to the next in a single block. This indicates weak magnetic coupling between the interfacial and volume magnetizations in GdN. The results are at variance with the much studied "model" multilayer system Gd/Fe, where magnetic order in the Gd-layer volume appears intrinsically only significantly below the Curie temperature of bulk Gd. Furthermore, magnetization reversal in the Gd layers in a magnetic field occurs gradually on a considerably larger length scale, only if they are sufficiently thick. (c) 2006 American Institute of Physics
X-ray magnetic circular dichroism at the Gd L-2,L-3 absorption edges in GdN layers: The influence of lattice expansion
No full textWe have measured core-level x-ray-absorption spectra and x-ray magnetic circular dichroism (XMCD) at the Gd-L-2,L-3 edges to characterize the low-lying Gd-5d derived conduction-band states in thin films of the 4f ferromagnet GdN with a unit-cell volume 8.6% above that of bulklike layers. The nonequilibrium structure is obtained by N+ plasma-assisted reactive sputter deposition at room temperature. The Curie temperature T-C, a key quantity for magnetism, amounts to only half the bulk value of similar to 60 K indicating a significant reduction of the effective exchange interaction between the 4f states. An intricate observation is that the ratio of the dichroic signal amplitudes in the lattice-expanded layers, parallel to L-3/L-2 parallel to, is up to three times higher than the value expected from the degeneracy of the 2p(3/2) and 2p(1/2) core states, which is observed for the bulklike layers. This is mainly due to a reduced L-2 XMCD amplitude. We suggest that the effect may be related to the different weight the crystal-field split Gd-5d final states (t(2g) and e(g)) have in the absorption process at the L-2 and L-3 edges, and to the special electronic band structure of this strongly correlated material and its modification upon lattice expansion. This hypothesis is supported by the observation that the L-2 absorption edge is shifted to lower energies upon ferromagnetic ordering while the L-3-edge position remains inert
Intrinsic and nonlocal Gilbert damping parameter in all optical pump-probe experiments
No full textThe study of magnetization dynamics on the femtosecond time scale is an important task for the implementation of future ultrafast spintronics. With the time resolution inherent using femtosecond laser pulses in all optical pump-probe experiments, the basic time constants of magnetic precessional modes as well as the energy dissipation processes, which determine the Gilbert damping, can be studied. The dominant magnetic relaxation modes for the thin Ni films have frequencies in the range of 1.5-13 GHz. The corresponding Gilbert damping parameter is found to be dependent on the precession mode. The alpha values range from 0.05 to 0.8 for highly damped modes. The nonlocal Gilbert damping due to evanescent spin currents and two-magnon scattering is studied for double layers Ni/Cr/Si(100) with varied Ni thicknesses. A large increase of the damping parameter for films with a thinner Ni layer is observed. (C) 2006 American Institute of Physics
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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