1,720,992 research outputs found
Hysteretic Synchronization in SpinTorque NanoContact Oscillators: a Micromagnetic Study
No full textSeveral experiments report the presence of finite jumps in the properties of spin-torque oscillators at room temperature, such as oscillation frequency and power as functions of current or field. On the basis of micromagnetic simulations, this paper links those experimental discontinuities to the changes in the curve slope numerically observed in the absence of thermal effects. Our numerical results show the key ingredient triggering this behavior is the presence of abrupt changes in the oscillation axis of the magnetization precession. We also predict that by fixing the bias point of the oscillator near those critical regions, it is possible to observe hysteretic synchronization. This result should be a key point in the design of nanoscale on-chip phase-locked loop receivers with improved sensitivity
Nanomagnetic logic with non-uniform states of clocking
No full textNanomagnetic logic transmits information along a path of nanomagnets. The basic mechanism to drive such a transmission, known as clocking, can be achieved by exploiting the spin-Hall effect (SHE), as recently observed in experiments on Ta/CoFeB/MgO multilayers (Bhowmik et al 2014 Nat. Nano 9 59). This paper shows the fundamental mechanism of the spin-Hall driven clocking by using a full micromagnetic framework and considering two different devices, Ta/CoFeB/MgO and Pt/CoFeB/MgO. The former is used for a direct comparison of the numerical results with the experiments while the latter permits the effect of the Dzyaloshinskii-Moriya interaction (DMI) in the clocking mechanism to be predicted. Results show that the clocking state is non-uniform and it is characterized by the presence of domains separated by Bloch (Neel) domain walls depending on the absence (presence) of the DMI. Our findings point out that for the design of nanomagnetic logic a full micromagnetic approach is necessary
A time-frequency analysis of electrical users by means of Fourier and Wavelet transforms
No full textAdvanced signal processing tools can provide significant information on power systems. In this field of research, the present paper illustrates a time-frequency analysis to detect some properties of the power required by different types of users. Fourier and Wavelet transforms, in particular, are the numerical instruments to reveal the periodicity of the power signals and their stationarity. Results point out that different types of users are characterized by different sets of non-stationary frequency contributions, which can identify the typology of user
Fourier, Wavelet, and Hilbert-Huang Transforms for Studying Electrical Users in the Time and Frequency Domain
Get PDFThe analysis of electrical signals is a pressing requirement for the optimal design of power distribution. In this context, this paper illustrates how to use a variety of numerical tools, such as the Fourier, wavelet, and Hilbert-Huang transforms, to obtain information relating to the active and reactive power absorbed by different types of users. In particular, the Fourier spectrum gives the most important frequency components of the electrical signals, and the wavelet analysis highlights the non-stationarity of those frequency contributions, whereas the Hilbert-Huang transform, by means of the Empirical Mode Decomposition, provides a more complete spectrum of frequencies
Magnetic Radial Vortex Stabilization and Efficient Manipulation Driven by the Dzyaloshinskii-Moriya Interaction and Spin-Transfer Torque
Get PDFSolitons are very promising for the design of the next generation of ultralow power devices for storage and computation. The key ingredient to achieving this goal is the fundamental understanding of their stabilization and manipulation. Here, we show how the interfacial Dzyaloshinskii-Moriya Interaction (IDMI) is able to lift the energy degeneracy of a magnetic vortex state by stabilizing a topological soliton with radial chirality, hereafter called radial vortex. It has a noninteger Skyrmion number S (0.5<|S|<1) due to both the vortex core polarity and the magnetization tilting induced by the IDMI boundary conditions. Micromagnetic simulations predict that a magnetoresistive memory based on the radial vortex state in both free and polarizer layers can be efficiently switched by a threshold current density smaller than 10^6 A/cm^2. The switching processes occur via the nucleation of topologically connected vortices and vortex-antivortex pairs, followed by spin-wave emissions due to vortex-antivortex annihilations
Micromagnetic study of spin-transfer-driven vortex dipole and vortex quadrupole dynamics
No full textMagnetic vortex and antivortex are nonuniform magnetization configurations that can be also achieved in spin-torque oscillators either isolated or as vortex-antivortex pair, namely vortex dipole. This paper shows a systematic micromagnetic study about the identification of soliton dynamics characterized by different skyrmion numbers. Our results show the excitation of both rotation and translation of vortex dipoles and rotating vortex quadrupoles. Those different scenarios can be achieved by changing the geometrical parameters of spin valve and the amplitude of external field. The origin of the different dynamical behaviors is explained within a micromagnetic framework
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
Computing with injection-locked spintronic diodes
No full textSpintronic diodes (STDs) are emerging as a technology for the realization of
high-performance microwave detectors. The key advantages of such devices are
their high sensitivity, capability to work at low input power, and compactness.
In this work, we show a possible use of STDs for neuromorphic computing
expanding the realm of their functionalities to implement analog
multiplication, which is a key operation in convolutional neural networks
(CNN). In particular, we introduce the concept of degree of rectification (DOR)
in injection-locked STDs. Micromagnetic simulations are used to design and
identify the working range of the STDs for the implementation of the DOR.
Previous experimental data confirm the applicability of the proposed solution,
which is tested in image processing and in a CNN that recognizes handwritten
digits.Comment: 21 pages, 6 figures, supplemental material includes 4 figure
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