229 research outputs found

    Anomalous Hall effect in ferromagnets with Gaussian disorder

    Get PDF
    Using the Kubo formalism we derived expressions and implemented the method for calculating the anomalous Hall conductivity (AHC) in ferromagnets with short-range Gaussian disorder directly from first-principles electronic structure of the perfect crystal. We used this method to calculate the AHC in bcc Fe, fcc Co, L1o-FePd, L1o-FePt as well as thin bcc Fe(001) films. Within our approach we can transparently decompose the conductivity into intrinsic (IC), side jump (SJ) and intrinsic skew-scattering (ISK) contributions. The existence of ISK, which originates from asymmetric Mott scattering but is clearly distinguishable from conventional skew-scattering in that it converges to a finite value in clean limit, was pointed out by Sinitsyn et al. [Phys. Rev. B 75, 045315 (2007)]. Here, we collect all contributions to the AHC in ferromagnets which result in "scattering-independent" AHE in clean limit, and analyze their relative magnitude from first principles calculations. By comparing our results to existing experiments we show that the Gaussian disorder is well suited to model various types of disorder present in real materials, to some extent including the effect of temperature. In particular, we show that in addition to intrinsic and side-jump AHE, the intrinsic skew-scattering can be a major player in determining the magnitude of the AHE in ferromagnets.Comment: 10 pages, 3 figure

    Scattering-Independent Anomalous Nernst Effect in Ferromagnets

    Get PDF
    Using the full-potential linearized augmented plane-wave method within the density functional theory, we compute all contributions to the scattering independent part of the thermoelectric conductivity tensor, namely the intrinsic contribution and the side-jump contribution. For the ferromagnetic materials bcc Fe, hcp Co, fcc Ni and L1_0 ordered alloys FePd and FePt, our investigations of the energy and temperature dependence of the intrinsic and side-jump contributions show that they are both of equal importance. Overall, our calculations are able to correctly reproduce the order of magnitude and sign of the experimentally measured signal, suggesting that the scattering independent part plays an important role in the anomalous Nernst effect of ferromagnets.Comment: 5 pages, 2 figures plus supplement, accepted for publication as a Rapid Communication in Physical Review

    Ab Initio Theory of Scattering-Independent Anomalous Hall Effect

    Get PDF
    We report on first-principles calculations of the side-jump contribution to the anomalous Hall conductivity (AHC) directly from the electronic structure of a perfect crystal. We implemented our approach for a short-range scattering disorder model within the density functional theory and computed the full scattering-independent AHC in elemental bcc Fe, hcp Co, fcc Ni, and L1o FePd and FePt alloys. The full AHC thus calculated agrees systematically with experiment to a degree unattainable so far, correctly capturing the previously missing elements of side-jump contributions, hence paving the way to a truly predictive theory of the anomalous Hall effect and turning it from a characterization tool to a probing tool of multi-band complex electronic band structures.Comment: PRL in pres

    Der blinde Fleck des Kritikers. Zu den 'Wahrheiten' einer Konstruktivismus-Rezeption

    Get PDF
    Konstruktivisten wie Heinz von Foerster provozieren mit der Feststellung, ObjektivitĂ€t sei die Illusion, daß Beobachtungen ohne jemanden möglich seien, der beobachtet. Wenn es aber Beobachter sind, die beobachten, dann hat jede Beobachtung sozusagen einen Eigenwert: Das, was der Beobachter von seinem Standpunkt aus sehen kann und was nicht. Dieses nicht Sichtbare ist der blinde Fleck jeder Beobachtung. Damit ist eine Grundbedingung jeder Wahrnehmung beschrieben, die zu reflektieren den journalistischen Alltag nicht gerade erleichtert. Praktischer ist es zu postulieren, daß Berichterstattung eine möglichst weitgehende AnnĂ€herung an die Ereignisse und damit an 'die RealitĂ€t' zum Ziel hat. Als ideales Rollenbild der Journalisten wird deshalb der "Vermittler" ausgerufen und so der Erwartungshorizont fĂŒr die PrimĂ€rfunktion der Medien beschrieben. (...)

    Anisotropy of spin relaxation and transverse transport in metals

    Full text link
    Using first principles methods we explore the anisotropy of the spin relaxation and transverse transport properties in bulk metals with respect to the direction of the spin quantization axis in paramagnets or of the spontaneous magnetization in ferromagnets. Owing to the presence of the spin-orbit interaction the orbital and spin character of the Bloch states depends sensitively on the orientation of the spins relative to the crystal axes. This leads to drastic changes in quantities which rely on interband mixing induced by the spin-orbit interaction. The anisotropy is particularly striking for quantities which exhibit spiky and irregular distribution in the Brillouin zone, such as the spin-mixing parameter or the Berry curvature of the electronic states. We demonstrate this for three cases: (i) the Elliott-Yafet spin-relaxation mechanism in paramagnets with structural inversion symmetry; (ii) the intrinsic anomalous Hall effect in ferromagnets; and (iii) the spin Hall effect in paramagnets. We discuss the consequences of the pronounced anisotropic behavior displayed by these properties for spin-polarized transport applications.Comment: Psi-k Highlight 111 (2012

    Das "Kommentariat" : Rolle und Status einer Öffentlichkeitselite

    Get PDF
    Im Mittelpunkt des WZB-Papers stehen die „Meinungsmacher“ der ĂŒberregionalen QualitĂ€tszeitungen in der Bundesrepublik. Die Kommentare dieser „Leitmedien“ wer-den im politischen System intensiv wahrgenommen. Die ThemenprĂ€ferenzen und Mei-nungen der Kommentatoren dienen als Hinweise auf allgemeine Stimmungen in der Bevölkerung und auf die Durchsetzbarkeit konkreter Entscheidungen. Auch in öffent-lichkeitstheoretischer Perspektive stellen Kommentatoren einen besonders herausgeho-benen „Sprecher“-Typus dar. Im Gegensatz zu anderen Sprechern, die um Medienauf-merksamkeit konkurrieren, besitzen Kommentatoren ein entscheidendes Privileg: sie produzieren nicht nur Themen und Meinungen; sie können selber dafĂŒr sorgen, dass ihre Äußerungen tatsĂ€chlich öffentlich werden. Angesichts der öffentlichkeitstheoreti-schen und politischen Bedeutung der Kommentatoren ĂŒberrascht, dass das „Kommenta-riat“ in der bisherigen Forschung eine merkwĂŒrdig unbeschriebene GrĂ¶ĂŸe geblieben ist. Auf der Basis einer schriftlichen Befragung und persönlicher GesprĂ€che mit Kommen-tatoren der Frankfurter Allgemeinen Zeitung, der SĂŒddeutschen Zeitung, der Frankfurter Rundschau, der Welt und der tageszeitung gibt diese Studie einen Einblick in die wich-tigsten Charakteristika dieser Sprechergruppe. Wer sind also die Meinungsmacher der deutschen QualitĂ€tspresse? Wie viele Journalisten umfasst diese Öffentlichkeitselite und welche sozio-kulturellen Profile kennzeichnen sie? Wie sehen die Zugangschancen aus? Handelt es sich um einen vergleichsweise offenen Kreis von Journalisten, die von Zeit zu Zeit kommentieren, oder um eine abgeschlossene Gruppe von Vordenkern der Nati-on, die dauerhaft und fast ausschließlich mit der Meinungsproduktion betraut ist? Was sind die Kriterien fĂŒr den Zugang zu dieser Öffentlichkeitselite und wie unterscheiden sich die Zeitungen in Hinblick auf die Zugangschancen? Und fĂŒhrt die Auswahl der Kommentatoren zu Themenspezialisierungen oder Meinungsoligopolen innerhalb und möglicherweise auch zwischen den Zeitungen?The WZB-paper focuses on the “opinion makers” of the national quality newspapers in Germany. The press commentaries are closely observed by the political system. The issues and opinions brought up in the opinion section serve as indicators for the general sentiment of the public and the popularity of certain policies. From a theoretical point of view, commentators are regarded as a very special type of actor in the public sphere. In contrast to other actors in public communication who have to compete for media atten-tion, they enjoy a significant privilege: Not only do they produce messages for public debate, they also decide which messages are eventually publicized. Considering their public and political influence it is rather surprising that neither sociology nor communi-cation research has investigated this group of communicators. This paper presents re-sults of a survey and in-depths-interviews with commentators of the Frankfurter Allgemeine Zeitung, SĂŒddeutsche Zeitung, Frankfurter Rundschau, Welt and tageszeitung and thus provides an insight into the characteristics of this group. Who are the “opinion makers” in the leading national quality newspapers? How many journalists belong to this elite of actors in the public sphere and what are their socio-cultural profiles? To what degree and how is access to the opinion section restricted? Do commentators form a closed circle of national masterminds permanently producing opinions or do they rep-resent a rather open group of journalists who among other articles also write commen-taries from time to time? What are the recruitment criteria for commentators and in which ways do the national broadsheets under study differ in terms of access gain? And finally: Does the selection of commentators lead to issue specialization or even opinion monopolies within and across the newspapers

    Scheduling science on television: A comparative analysis of the representations of science in 11 European countries

    Get PDF
    While science-in-the-media is a useful vehicle for understanding the media, few scholars have used it that way: instead, they look at science-in-the-media as a way of understanding science-in-the-media and often end up attributing characteristics to science-in-the-media that are simply characteristics of the media, rather than of the science they see there. This point of view was argued by Jane Gregory and Steve Miller in 1998 in Science in Public. Science, they concluded, is not a special case in the mass media, understanding science-in-the-media is mostly about understanding the media (Gregory and Miller, 1998: 105). More than a decade later, research that looks for patterns or even determinants of science-in-the-media, be it in press or electronic media, is still very rare. There is interest in explaining the media’s selection of science content from a media perspective. Instead, the search for, and analysis of, several kinds of distortions in media representations of science have been leading topics of science-in-the-media research since its beginning in the USA at the end of the 1960s and remain influential today (see Lewenstein, 1994; Weigold, 2001; Kohring, 2005 for summaries). Only a relatively small amount of research has been conducted seeking to identify factors relevant to understanding how science is treated by the mass media in general and by television in particular. The current study addresses the lack of research in this area. Our research seeks to explore which constraints national media systems place on the volume and structure of science programming in television. In simpler terms, the main question this study is trying to address is why science-in-TV in Europe appears as it does. We seek to link research focussing on the detailed analysis of science representations on television (Silverstone, 1984; Collins, 1987; Hornig, 1990; Leon, 2008), and media research focussing on the historical genesis and current political regulation of national media systems (see for instance Hallin and Mancini, 2004; Napoli, 2004; Open Society Institute, 2005, 2008). The former studies provide deeper insights into the selection and reconstruction of scientific subject matters, which reflect and – at the same time – reinforce popular images of science. But their studies do not give much attention to production constraints or other relevant factors which could provide an insight into why media treat science as they do. The latter scholars inter alia shed light on distinct media policies in Europe which significantly influence national channel patterns. However, they do not refer to clearly defined content categories but to fairly rough distinctions such as information versus entertainment or fictional versus factual. Accordingly, we know more about historical roots and current practices of media regulation across Europe than we do about the effects of these different regimes on the provision of specific content in European societies

    Macht und Verantwortung der Medien : Bamberger Hegelwoche 2007

    Get PDF
    Macht und Verantwortung der Medien. Wir EuropĂ€er haben die freiheitliche Gesellschaft in der AufklĂ€rung postuliert und in einem langwierigen, auch durch RĂŒckschlĂ€ge verzögerten Entwicklungsprozess durchgesetzt. Sie hat nur dann Bestand, wenn alle BĂŒrger in gleicher Weise aufgeklĂ€rt sind und sich auf einfache Art und Weise diejenigen Informationen beschaffen können, die sie benötigen, um ihrer Aufgabe als SouverĂ€n des Staates gerecht zu werden. Aus gutem Grund bezeichnen wir daher die Medien auch als vierte Gewalt im Staat. Wenn sie behindert wird oder wenn sie versagt, ist unsere Gesellschaftsordnung gefĂ€hrdet. Daher mĂŒssen wir immer wieder kritisch hinterfragen, ob unsere Medien den an sie gerichteten Auftrag noch erfĂŒllen – ein Auftrag zwischen Anspruch und Wirtschaftlichkeit, zwischen Pressefreiheit und Zensur
    • 

    corecore