1,721,013 research outputs found
Topological, non-topological instanton droplets driven by spin-transfertorque in materials with perpendicular magnetic anisotropy and Dzyaloshinskii–Moriya interaction
Get PDFThe interfacial Dzyaloshinskii–Moriya Interaction can modify the topology of droplets excited by a
localized spin-polarized current. Here, we show that, in addition to the stationary droplet excitations
with skyrmion number either one (topological) or zero (non-topological), there exists, for a fixed
current, an excited mode with a non-stationary time behavior. We call this mode “instanton droplet”,
which is characterized by time domain transitions of the skyrmion number. These transitions are
coupled to an emission of incoherent spin-waves that can be observed in the frequency domain as
a source of noise. Our results are interesting from a fundamental point of view to study spin-wave
emissions due to a topological transition in current-driven systems, and could open the route for
experiments based on magnetoresistance effect for the design of a further generation of nanoscale
microwave oscillators
Modulation of Asymmetric Magnetic Domain-Wall Motion via Noncolinear Interlayer Exchange Coupling
No full textThe search of scalable approach to design field-free deterministic switching is currently a key challenge. Here, we investigate current and magnetic driven magnetization switching in a T-type magnetic heterojunction with a structure composed by a hybrid synthetic antiferromagnet (SAF) Co/Ta/CoTb/Pt, where the bottom Co layer has in-plane magnetic anisotropy (IMA) and the top CoTb layer has perpendicular magnetic anisotropy (PMA). The interlayer exchange coupling (IEC) interaction allows a tilted easy axis of the perpendicular CoTb layer. The main result achieved is the field-free magnetization switching driven by spin-orbit torque (SOT) with a switching direction (clockwise or counterclockwise), which can be controlled by the in-plane direction of the Co magnetization. Meanwhile, we demonstrate that the IEC also induces the asymmetric bubble expansion in the CoTb layer in field-driven experiments and favors the propagation of the domain walls (DWs) with internal magnetization antiparallel to the in-plane IEC field. Our results demonstrate versatile control of the DW motion by noncollinear IEC, which paves a potential way for designing energy-efficient spintronic memory and logic devices, as well as provides a promising and high-efficiency approach for detecting the IEC type by magneto-optical Kerr effect (MOKE) in T-type magnetic heterojunction
Variability-Aware Analysis of Hybrid MTJ/CMOS Circuits by a Micromagnetic-Based Simulation Framework
No full textMagnetic tunnel junctions (MTJs) are attracting an increasing interest due to their potentiality for high-density nonvolatile memories. However, some issues need to be opportunely considered in the design and optimization of hybrid MTJ/CMOS circuits, such as the stochastic nature of the MTJ switching, the high write energy consumption and the susceptibility to process variations. In this paper, we evaluate the impact of both MTJ and CMOS variability on the performance of basic hybrid MTJ/CMOS circuits in state-of-the-art nanoscale technologies. To this purpose, we exploit a simulation framework combining micromagnetic and electrical simulations. Full micromagnetic simulations are used to predict the MTJ behavior in terms of magnetoresistance-current hysteresis loop and statistical distribution of the switching delay as a function of the applied current. Those data are used to set up a look-up-table-based MTJ Verilog-A model to be used in commercial electrical simulators. Considering an MTJ with a diameter of 30 nm and a 28-nm fully-depleted silicon-on-insulator CMOS technology, we have exploited the above simulation framework to perform a variability-aware analysis on the write operation of a 1-MTJ writing circuit for nonvolatile flip-flops and a 256 x 256 STT-MRAM array. Our results show that the voltage scaling can be a promising approach for energy minimization in hybrid MTJ/CMOS circuits at the expense of larger area
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Unified Framework for Micromagnetic Modeling of Ferro-, Ferri-, and Antiferromagnetic Materials at Mesoscopic Scale: Domain Wall Dynamics as a Case Study
No full textWe introduce a formulation of a two-sublattice micromagnetic model, which can describe the statics and dynamics of ferromagnets, antiferromagnets, and ferrimagnets. Such a formulation is based on the normalization of exchange, Dzyaloshinskii–Moriya interaction, and anisotropy parameters with respect to the square modulus of the saturation magnetization for each sublattice. We show a study of the statics and dynamics of domain walls (DWs) focusing on antiferromagnets and ferrimagnets because of their potential ultrafast performance in terms of dynamics and robustness against external magnetic perturbations. Our results show a direction to design DW-based nanodevices in ferrimagnets with a superlinear velocity increasing as a function of the spin–orbit torque amplitude by working near, but still below, the threshold current for the excitation of self-oscillations
Spintronic temperature nanosensor based on the resonance response of a skyrmion-hosting magnetic tunnel junction
No full textThe increasing need for efficient thermal management in nanoelectronics requires innovative thermal sensing solutions, as conventional sensors often exhibit nonlinear responses, low sensitivity, and complex calibration. We predict a temperature dependence in the response of existing skyrmion-based spintronic diodes and propose their use as nanoscale thermal sensors. These devices leverage magnetic skyrmions - topologically protected spin textures known for their robustness, nanoscale dimensions, and low-power dynamics. We demonstrate high thermal sensitivity with a linear temperature response over a wide range. This linearity, observed in both the amplitude and frequency of the skyrmion excitation, ensures redundancy that enables precise and reliable temperature measurement. In addition, the use of multilayer systems enhances the sensitivity and robustness of the device. These results provide a foundation for skyrmion-based caloritronic devices with promising applications in spintronic sensors, thermal management, nanoelectronics, and skyrmion-caloritronics
Skyrmions in synthetic antiferromagnet nanorings for electrical signal generation
No full textCurrent-driven magnetic skyrmions show promise as carriers of information bits in racetrack magnetic memory applications. Specifically, the utilization of skyrmions in synthetic antiferromagnetic (SAF) systems is highly attractive due to the potential to suppress the skyrmion Hall effect, which causes a transverse displacement of driven skyrmions relative to the shift direction. In this study, we demonstrate, through analytical calculations and micromagnetic simulations, that in the case of a nanoring geometry, current-driven skyrmions achieve a stable circular motion with a constant frequency, which is a prerequisite for a skyrmion-based clock device. Notably, the operational frequency in a SAF nanoring surpasses that in a bilayer ferromagnetic-heavy metal nanoring and lies in the GHz regime for current densities of 40 × 10 10 A m − 2 . We also find that the performance of skyrmions in SAF nanorings is comparable to that of radial Néel domain walls for low current densities (approximately 30 × 10 10 A m − 2 ) and low skyrmion densities (Nsk ≈ 6). Additionally, we introduce a novel skyrmionic three-phase AC alternator based on a SAF nanoring, which operates at frequencies in the GHz regime. Our findings underscore the potential of SAF nanorings as constituent materials in clock devices with tunable frequencies operating in the GHz regime
Variations on the Author
Get PDF“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
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