1,721,014 research outputs found
Analytical and Micromagnetic Study of Nonlinear Amplitude Modulation in Spintronic Modulators
No full textA previous universal model of "combined" frequency-amplitude nonlinear modulation has been used to describe the spin-wave dynamics observed in spin-transfer oscillators. In that case, it was shown that it is not possible to obtain a pure frequency modulation process because the strict nonlinear relationship existing between the characteristic parameters of the oscillator yields a non-negligible amplitude modulation process to take place simultaneously. Here, we demonstrate that there exists a particular configuration in which a spin-torque oscillator behaves as a "pure" nonlinear amplitude modulator. For the case of a nano-contact geometry, for example, such a condition implies the usage of an external out-of-plane bias field directed along the critical angle at which the frequency tunability coefficient T = partial derivative f/partial derivative I vanishes. In all those cases in which this coefficient is not zero, the previous combined process takes place. The phenomenon is first analyzed by developing an analytical model which describes the structure of the frequency spectrum of a nonlinearly amplitude modulated signal. Results of this approach are finally compared with those of micromagnetic investigations, carried out in time and frequency domains, deriving an excellent agreement
Micromagnetic Analysis of Nonlinear Dynamics in Spintronic Analog Modulators
No full textThe simultaneous action of dc and ac spin-polarized current traversing a magnetic nanocontact device results in a combined amplitude-frequency nonlinear modulation process, a promising application of spin-transfer oscillators. A micromagnetic analysis of the nonlinear magnetization dynamics occurring in such devices is carried out in both spatial and frequency domain. Numerical results show that the proposed combined modulation scheme affects the amplitude of the sidebands as well as their phase, and remark a substantial difference with respect to the properties exhibited by a classical linear modulator. Further investigations performed as function of the frequency of the modulating signal allow to establish that, when the modulating frequency approaches the carrier one, no modulation occurs and a frequency pulling, typical of injection locking phenomena, takes place instead
Robustness of using degree of match in performing analog multiplication with spin-torque oscillators
No full textThe multiplication operation is one of the most used, but also one of the most energy-expensive operations in digital systems. Here, we focus on a promising strategy to perform the analog multiplication which is based on the use of two coupled spin-torque oscillators (STOs) using the concept of Degree of Match (DOM). The study is based on the theory of non-linear auto-oscillators with negative damping universally used for STOs. The robustness of the DOM is assessed with respect to the variability and noise perturbances parameters
Magnetic solitons driven by spin-based phenomena: A review on their features and potentialities
No full textMagnetic solitons are localized magnetization configurations which can be stabilized in both conservative and dissipative systems. They can be nucleated by means of the spin-transfer torque starting from a uniform magnetization state and they can exist as static or dynamical states. They can be classified according to their topology, namely to their skyrmion number. Here, we summarize the main features of three kinds of solitons (vortexes, bubbles, and skyrmions), pointing out their most promising technological applications
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
Scalable synchronization of spin-Hall oscillators in out-of-plane field
Full text linkA strategy for a scalable synchronization of an array of spin-Hall oscillators (SHOs) is illustrated. In detail, we present the micromagnetic simulations of two and five SHOs realized by means of couples of triangular golden contacts on the top of a Pt/CoFeB/Ta trilayer. The results highlight that the synchronization occurs for the whole current region that gives rise to the excitation of self-oscillations. This is linked to the role of the magnetodipolar coupling, which is the phenomenon driving the synchronization when the distance between oscillators is not too large. Synchronization also turns out to be robust against geometrical differences of the contacts, simulated by considering variable distances between the tips ranging from 100 nm to 200 nm. Besides, it entails an enlargement of the radiation pattern that can be useful for the generation of spin-waves in magnonics applications. Simulations performed to study the effect of the interfacial Dzyaloshinskii-Moriya interaction show nonreciprocity in spatial propagation of the synchronized spin-wave. The simplicity of the geometry and the robustness of the achieved synchronization make this design of array of SHOs scalable for a larger number of synchronized oscillators
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
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