Two-step Switching Research Articles

SOT-MRAM Elements Based on Spin Hall Effect: Macrospin Model of Two-Step Switching Control

SOT-MRAM Elements Based on Spin Hall Effect: Macrospin Model of Two-Step Switching Control

Light-Induced, Structural Matrix Guided Stepwise Spin-State Switching in 3d-5d Molecular Assembly.

A new iron(II) molecular complex {[W(CN)8][Fe(bik*)3]2}BF4·7H2O·1.5CH3OH (1.7H2O·1.5CH3OH) was synthesized using a versatile octacyanotungstate(V) building block and N-donor bidentate ligand (bik* = bis(1-ethyl-1H-imidazol-2-yl)ketone) and detailed characterizations were carried out. The crystal structure of 1.7H2O·1.5CH3OH is composed of an ionic salt from one anionic [W(CN)8]3- unit, two isolated cationic [Fe(bik*)3]2+ units, and one BF4- counteranion in the asymmetric unit. Magnetic studies of 1.7H2O·1.5CH3OH display interesting two-step reversible thermo-induced spin-state switching and the partially desolvated form 1.7H2O shows a photomagnetic effect at low temperatures. Additionally, the physical properties of 1.7H2O·1.5CH3OH were compared with the monomeric unit of {[Fe(bik*)3]2}·4ReO4·H2O (2.H2O) and detailed photophysical investigations were also performed to study the effect of a structural matrix {[W(CN)8]3- and ReO4- unit} on the spin-state switching properties of the [Fe(bik*)3]2+ unit in both systems (1.7H2O·1.5CH3OH and 2.H2O).

Adaptive pathfinding by nucleokinesis during amoeboid migration.

Motile cells encounter microenvironments with locally heterogeneous mechanochemical composition. Individual compositional parameters, such as chemokines and extracellular matrix pore sizes, are well known to provide guidance cues for pathfinding. However, motile cells face diverse cues at the same time, raising the question of how they respond to multiple and potentially competing signals on their paths. Here, we reveal that amoeboid cells require nuclear repositioning, termed nucleokinesis, for adaptive pathfinding in heterogeneous mechanochemical micro-environments. Using mammalian immune cells and the amoeba Dictyostelium discoideum, we discover that frequent, rapid and long-distance nucleokinesis is a basic component of amoeboid pathfinding, enabling cells to reorientate quickly between locally competing cues. Amoeboid nucleokinesis comprises a two-step polarity switch and is driven by myosin-II forces that readjust the nuclear to the cellular path. Impaired nucleokinesis distorts path adaptions and causes cellular arrest in the microenvironment. Our findings establish that nucleokinesis is required for amoeboid cell navigation. Given that many immune cells, amoebae, and some cancer cells utilize an amoeboid migration strategy, these results suggest that nucleokinesis underlies cellular navigation during unicellular biology, immunity, and disease.

Macroprudential and Monetary Policy Interactions and Coordination in South Africa: Evidence from Business and Financial Cycle Synchronisation

The article reports on the interactions and possibility of coordination between macroprudential and monetary policies in South Africa, based on business and financial cycles synchronisation. To this end, relying on financial and economic time series indicators spanning the period 2000M01–2018M12, a two-step Markov switching dynamic factor model was adopted for the measurement of composite indices, while both the dynamic conditional correlations and asymmetric generalised dynamic conditional correlations models were adopted for synchronisation analysis, together with the Metcalfe scale of coordination. The empirical evidence obtained is such that, under conditions of financial and real economic stress in South Africa, when there is crisis management rather than crisis prevention, macroprudential policy and monetary policy decisions are complementary. Therefore, there will be limited/no need for coordination between the two policy decisions. However, under normal times when there is crisis prevention rather than management, macroprudential policy and monetary policy decisions are noncomplementary; hence, the greatest degree of coordination is warranted, even though it might not be easy. Therefore, we conclude that it is possible to the coordinate the conduct of macroprudential, and monetary policies based on the synchronicity of business and financial cycles.

Ligand Modifications Produce Two-Step Magnetic Switching in a Cobalt(dioxolene) Complex.

Mononuclear monodioxolene valence tautomeric (VT) cobalt complexes typically exist in their low spin (l.s.) CoIII (cat2- ) and high spin (h.s.) CoII (sq⋅- ) forms (cat2- =catecholato, and sq⋅- =seminquinonato forms of 3,5-di-t Bu-1,2-dioxolene), which reversibly interconvert via temperature-dependent intramolecular electron transfer. Typically, the remaining four coordination sites on cobalt are supported by a tetradentate ligand whose properties influence the temperature at which VT occurs. We report that replacing one chelating pyridyl arm of tris(2-pyridylmethyl)amine (tpa) with a weaker field ortho-anisole moiety facilitates access to a third magnetic state, and examine a series of related complexes. Variable temperature crystallographic, magnetic, calorimetric, and spectroscopic studies support that this third state is consistent with l.s. CoII (sq⋅- ). Thus, our ligand modifications not only provide access to the VT transition from l.s. CoIII (cat2- ) to l.s. CoII (sq⋅- ), but at higher temperatures, the complex undergoes spin crossover from l.s. CoII (sq⋅- ) to h.s. CoII (sq⋅- ), representing the first example of two-step magnetic switching in a mononuclear monodioxolene cobalt complex. We hypothesize that ligand dynamicity may facilitate access to the rarely observed l.s. CoII (sq⋅- ) intermediate state, suggesting a new design criterion in the development of stimulus-responsive multi-state molecular switches.

Design, Modelling and Optimization of a High Power Density Axial Flux SRM with Reduced Torque Ripple for Electric Vehicles

Switched reluctance machines (SRMs) are potential candidates for use in the propulsion systems of electric vehicles. However, they suffer from low power density and high torque ripple. In this paper, a segmented rotor double-sided axial flux SRM (DSAFSRM) is chosen for detailed analysis. A hybrid design algorithm is proposed to take the effects of iron non-linearity into account. The proposed design procedure benefits from simplicity and high accuracy at the same time. A two-step optimization procedure is presented which minimizes the torque ripple of the DSAFSRM without jeopardizing its efficiency. The torque ripple is reduced from 120% to 35% after optimization. In the two-step optimization procedure, both geometrical and switching related parameters are investigated. Moreover, a double-sided radial flux SRM is designed and compared with the proposed DSAFSRM in terms of torque ripple, average torque, efficiency and power density. The results indicate superior performance of the optimized DSAFSRM, especially in terms of average torque, which is 26% higher than the torque produced by the double-sided radial flux SRM.

A novel AD theranostic platform with NIR-II laser controlled drug release and real-time monitoring of therapeutic outcomes

There is a long-standing lack of monitoring of Alzheimer's disease (AD) treatment. Imaging-guided dynamic monitoring of neurological disease treatment can provide a basis for sustained treatment, reflecting the outcomes of treatment and guiding the adjustment of therapy strategies. Here, by ingeniously using a second near-infrared (NIR-II) laser twice in tandem, we designed an AD theranostic nanoplatform with real-time monitoring of AD therapeutic outcomes. Upon first being irradiated with a 1064 nm laser, it realizes the light-controlled delivery of nanoparticles for valid antioxidant therapy. Notably, with secondary irradiation, the presence of AβO and Ca2+ triggered the DNA nanomachine, causing the fluorescent signal to recover. Using a two-step series switch based on thermodynamics, the platform can not only differentiate AD mice from wild-type mice but also provide guidance for the treatment of AD via monitoring the degree of intracellular calcium overload in the brain. Results suggest that the degree of calcium overload is negatively correlated with treatment outcome and can be used as a prognostic indicator for precision medicine. This method provides an image-based non-invasive strategy for early prognosis prediction of AD treatment, which is helpful for future precision medicine treatment planning and prognosis stratification.

Analysis and Reduction of Current and Voltage Ripple in DC Link for Three-Level NPC Inverter-Fed Dual Three-Phase Motor Drives

In this article, switching strategies for dc-link current and voltage ripple reduction have been studied. The considered topology is a neutral-point clamped three-level (NPC-3L) inverter feeding a dual three-phase permanent-magnet synchronous motor (PMSM). The mechanisms of dc-link current and voltage ripple generation in an NPC-3L inverter-fed PMSM drive are analyzed in detail. Then, a two-step collaborative switching strategy is proposed, where the optimum switching sequences, including opposite small vectors, are applied in the two inverters collaboratively. Furthermore, the switching vectors of two inverters are rearranged in the sequence of their corresponding dc-link capacitor currents so that the overlapping of their peaks is avoided. Consequently, both the voltage ripple and current ripple in the dc-link capacitors are mitigated with the proposed two-step collaborative switching strategy. For the midpoint voltage of the NPC-3L inverter, the amplitude of fluctuation is reduced under low modulation index operation, while the high-frequency harmonic components are mitigated under high modulation index operation. The experimental results are given to verify the validity of the theoretical analysis and the proposed switching strategy.

Discrete Multi-Objective Switching Topology Sliding Mode Control of Connected Autonomous Vehicles With Packet Loss

Information flow topology is crucial in the control of connected autonomous vehicles. It has a substantial influence on the platoon's performance, especially in scenarios with imperfect communication. To address this issue, this study provides a real-time switching topology technique for improving the platoon's performance under various types of imperfect communication situations and constant packet dropout rates. First, a discrete sliding mode controller with a double power reaching law is designed for a nonlinear heterogeneous vehicle dynamic model with packet loss. Then, Lyapunov analysis is applied to ensure the platoon's stability and string stability. Finally, a two-step switching topology framework is introduced. The first step is to design an offline Pareto optimal topology search with some predicted imperfect communication scenarios, where the platoon's tracking ability, fuel consumption, and driving comfort are optimised using a multi-objective evolutionary algorithm based on decomposition with two opposing adaptive mechanisms. In the second step, the optimal topology is switched and selected in real-time from among the previously acquired Pareto optimal topology candidates, to reduce the control cost. To validate the proposed approach, numerical simulations are conducted. According to the results, compared to a standard robust sliding mode controller, the suggested technique enhances platoon tracking ability by 97.73 percent, fuel efficiency by 9.96 percent, and driving comfort by 20.18 percent, respectively.

Mechanistic and Kinetic Analysis of Perovskite Memristors with Buffer Layers: The Case of a Two-Step Set Process.

With the increasing demand for artificially intelligent hardware systems for brain-inspired in-memory and neuromorphic computing, understanding the underlying mechanisms in the resistive switching of memristor devices is of paramount importance. Here, we demonstrate a two-step resistive switching set process involving a complex interplay among mobile halide ions/vacancies (I-/VI+) and silver ions (Ag+) in perovskite-based memristors with thin undoped buffer layers. The resistive switching involves an initial gradual increase in current associated with a drift-related halide migration within the perovskite bulk layer followed by an abrupt resistive switching associated with diffusion of mobile Ag+ conductive filamentary formation. Furthermore, we develop a dynamical model that explains the characteristic I-V curve that helps to untangle and quantify the switching regimes consistent with the experimental memristive response. This further insight into the two-step set process provides another degree of freedom in device design for versatile applications with varying levels of complexity.

Fourfold magnetic anisotropy induced in CoFeB/IrMn bilayers by interfacial exchange coupling

Exchange bias (EB) occurring in ferromagnetic (FM)/antiferromagnetic (AFM) bilayers conventionally can lead to a unidirectional magnetic anisotropy () as well as an accompanied uniaxial magnetic anisotropy (). We observed an additional fourfold magnetic anisotropy () induced by interfacial exchange coupling in amorphous CoFeB/epitaxial IrMn bilayers with an EB. Because of the combined effect of the three kinds of magnetic anisotropies, one- and two-step magnetic switching processes were observed at different magnetic field orientations, which usually appear in single-crystal FM layer with an intrinsic magnetocrystalline anisotropy but not in amorphous FM layer. The angular dependent magnetic switching fields can be nicely fitted by a phenomenological model based on domain wall nucleation and propagation with the in-plane along <100>. The ferromagnetic resonance measurements indicate that the specific strength of for EB along [100] is larger than that for EB along [110]. The induced can be understood by considering two types of AFM domains caused by both monatomic steps and defects and their induced net uncompensated spins along the in-plane <100> axes. The different dependence of on the EB direction are because of the different effects of growth magnetic field on the presence of AFM domains.

Fixed-time and prescribed-time synchronization of quaternion-valued neural networks: A control strategy involving Lyapunov functions

A control strategy containing Lyapunov functions is proposed in this paper. Based on this strategy, the fixed-time synchronization of a time-delay quaternion-valued neural network (QVNN) is analyzed. This strategy is extended to the prescribed-time synchronization of the QVNN. Furthermore, an improved two-step switching control strategy is also proposed based on this flexible control strategy. Compared with some existing methods, the main method of this paper is a non-decomposition one, does not contain a sign function in the controller, and has better synchronization accuracy. Two numerical examples verify the above advantages.

Near room temperature stepwise spin state switching and photomagnetic effect in a mixed-valence molecular square.

A two-step thermo-induced spin-state switching was observed in a cyanide-bridged [Fe2Fe2] molecular square complex, {[Fe(pzTp)(CN)3]2[Fe(L)2]2}[Fe(pzTp)(CN)3]2·4CH3OH·2H2O [1·4MeOH·2H2O; pzTp = tetrakis(pyrazol-1-yl)borate and L = bis(1-ethylimidazol-2-yl)ketone (bik*)], which was characterized fully by single-crystal X-ray diffraction, (photo)magnetic measurements, and spectroscopic techniques. 1·4MeOH·2H2O exhibited a two-step thermo-induced spin transition with T1/2 (1) ↑ = 306 K and T1/2 (2) ↑ = 370 K converting the low-temperature ground state, {[(FeIIILS)2(FeIILS)2](FeIIILS)2} into the high-temperature state, {[(FeIIILS)2(FeIIHS)2](FeIIILS)2} via a stable intermediate phase. The desolvated phase, 1 also exhibited a gradual but reversible thermo-induced spin state change with a T1/2 value of 190 K, significantly shifted to a lower temperature. It also exhibited photo-induced spin-state switching at 20 K with the TLIESST value of 60 K.

Control-oriented dynamic process optimization of solid oxide electrolysis cell system with the gas characteristic regarding oxygen electrode delamination

Fast response, strong reliability, and high efficiency as the critical objectives of a solid oxide electrolysis cell (SOEC) system, which requires the system to operate under optimal operating conditions and switching manners. Therefore, various research has been carried out on its characteristic security. Most of them focus on the thermal characteristics security without further considering the security of gas characteristics regarding oxygen electrode delamination. However, this is one of the most critical degradations of SOEC. Herein, a novel SOEC system dynamic model with the gas characteristic regarding oxygen electrode delamination is proposed for the first time to optimize operation. Specially, the advantages are discussed through the optimization analysis of both the secure operation range regarding certain operating conditions and the steady-state operating points of the system. Subsequently, the dynamic process constraints of oxygen electrode delamination, fuel starvation, and power fast tracking during dynamic switching are investigated. The feasibilities of multi-step, parabola, and ramp schemes in solving the problems above are also evaluated. The outcomes show that the ramp scheme is preferred. Furthermore, the priority issue between oxygen electrode delamination and fuel starvation is studied, and corresponding dynamic process optimization strategies are developed for high and low initial power with a two-step switching method. After that, the dynamic process optimizations of two representative cases are investigated in detail. The optimization results show that the system efficiency is increased, and the safe ramp duration under the low initial power is significantly shortened. The findings of this study could provide a basis for developing control strategies for SOEC systems with fluctuating energy input.

Ta thickness effect on field-free switching and spin–orbit torque efficiency in a ferromagnetically coupled Co/Ta/CoFeB trilayer

Current induced spin–orbit torque (SOT) switching of magnetization is a promising technology for nonvolatile spintronic memory and logic applications. In this work, we systematically investigated the effect of Ta thickness on the magnetic properties, field-free switching and SOT efficiency in a ferromagnetically coupled Co/Ta/CoFeB trilayer with perpendicular magnetic anisotropy. We found that both the anisotropy field and coercivity increase with increasing Ta thickness from 0.15 nm to 0.4 nm. With further increase of Ta thickness to 0.5 nm, two-step switching is observed, indicating that the two magnetic layers are magnetically decoupled. Measurements of pulse-current induced magnetization switching and harmonic Hall voltages show that the critical switching current density increases while the field-free switching ratio and SOT efficiency decrease with increasing Ta thickness. Both the enhanced spin memory loss and reduced interlayer exchange coupling might be responsible for the β DL decrease as the Ta spacer thickness increases. The studied structure with the incorporation of a CoFeB layer is able to realize field-free switching in the strong ferromagnetic coupling region, which may contribute to the further development of magnetic tunnel junctions for better memory applications.

Ferroelectric diode characteristic and tri-state memory in self-assembled BiFeO3 nanoislands with cross-shaped domain structure

Exotic polarization domain configurations in BiFeO3 nanoislands have recently been achieved, promising for exploring next-generation nanoelectronics. Here, different from the earlier reported BiFeO3 nanoislands with a very thin cross-shaped domain wall on LaAlO3 substrates, we observed the cross-shaped domains with a downward polarization separating quad-domains with an upward polarization, which is confirmed by spherical aberration corrected scanning transmission electron microscopy and piezoresponse force microscopy. Interestingly, the cross- and quad-domains show diode-like transport behaviors but with different rectification directions owing to their different polarization orientations. Specifically, an intriguing two-step ferroelectric polarization switching can be realized, which locally results in a tri-state nonvolatile memory. These results broaden the understanding of the interesting polarization configurations in BiFeO3 nanoislands and highlight their potential as high-density information storage.

Consensus of Nonlinear Multiagent Systems With Aperiodic Intermittent Communications via Nonfragile Tracking Protocol

In this article, the problem of nonfragile tracking protocol design for high-order multiagent systems with Lipschitz-type node dynamics is investigated. Considerations are that the network is subject to aperiodic intermittent communications and the in-neighboring agents’ interactions switch in a directed graphs set, in which each element contains a directed spanning tree. The zero-order holder is employed to keep the local information from in-neighboring agents as the network communications are out of action. By virtue of a proposed two-step switching mechanism, one equivalently casts the concerned consensus tracking issue into asymptotically stabilizing a class of uncertain switched time-delay systems. Taking advantage of algebraic graph theory, Lyapunov–Krasovskii stability analysis, and robust nonfragile control approach, it is proved that the nonfragile consensus tracking can be achieved if a group of linear matrix inequalities are feasible and, for each time interval, the communication rate is larger than a threshold value. Numerical examples demonstrate the effectiveness of the theoretical results.

Improved Multibit Storage Reliability by Design of Ferroelectric Modulated Antiferroelectric Memory

In this article, we presented a new concept of ferroelectric (FE) modulated antiferroelectric (AFE) memory with independent two-step state switching and large polarization as a promising option for multibit storage in advanced technology nodes. Based on the Landau–Ginzburg–Devonshire (LGD) theory, four nonvolatile states of AFE with the built-in field can be obtained, and the step-by-step switching among four states was successfully simulated through pulse engineering; then, stable nonvolatile 2-bit storage was experimentally demonstrated in FE/AFE/FE capacitor device, and 0.97-MV/cm bipolar built-in field introduced by FE polarization switching was extracted. The FE + AFE device showed double-peak coercive electric field ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${E}_{c}$ </tex-math></inline-formula> ) distribution and large remanent polarization ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${P}_{r}$ </tex-math></inline-formula> ) of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$16.9 ~\mu \text{C}$ </tex-math></inline-formula> /cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> with good process stability. Finally, benefitting from the independently step-by-step switching and large density of effective FE domain, the improved multibit storage reliability was verified by kinetic Monte Carlo (KMC) modeling compared to conventional multibit technology.

Design and fabrication of Co2FeSi/Pt multilayers with perpendicular magnetic anisotropy

A series of multilayers consisting of Co2FeSi (CFS) and Pt are sputtered. Perpendicular magnetic anisotropy (PMA) is demonstrated in the CFS/Pt multilayers with CFS thickness in the range of 0.4 ∼ 1.0 nm. The individual thicknesses of Pt spacer and Co2FeSi layer as well as interface numbers are shown to strongly affect PMA. Two-step switching is observed in the multilayers with 8 nm Pt spacer, showing typically decoupled feature. The effective perpendicular anisotropy energy is determined to be in the order of 106 erg/cm3. The interfacial perpendicular anisotropy energy density is estimated to be 0.32 erg/cm2. The magnetic reversal with multi-domain feature is observed with increasing interface number. Sufficiently large saturation magnetization is derived from the multilayers with various repetitions. The thickness of magnetic dead layer is found to increase with the number of interface, which may be ascribed to more interdiffusion occurring at the multi-interfaces. Our results provide some useful information for the design and development of spintronic devices based on CFS/Pt multilayers.

Manipulation of spin orientation via ferroelectric switching in Fe-doped Bi2WO6 from first principles

Atomic-scale control of spins by electric fields is highly desirable for future technological applications. Magnetically doped Aurivillius-phase oxides present one route to achieve this, with magnetic ions substituted into the ferroelectric structure at dilute concentrations, resulting in spin-charge coupling. However, there has been minimal exploration of the ferroelectric switching pathways in this materials class, limiting predictions of the influence of an electric field on magnetic spins in the structure. Here, we determine the ferroelectric switching pathways of the end member of the Aurivillius phase family, ${\mathrm{Bi}}_{2}{\mathrm{WO}}_{6}$, using a combination of group theoretic analysis and density functional theory calculations. We find that in the ground state $P{2}_{1}ab$ phase, a two-step switching pathway via $C2$ and $Cm$ intermediate phases provides the lowest energy barrier. Considering iron substitutions on the W site in ${\mathrm{Bi}}_{2}{\mathrm{WO}}_{6}$, we determine the spin easy axis. By tracking the change in spin directionality during ferroelectric switching, we find that a ${90}^{\ensuremath{\circ}}$ switch in the polarization direction leads to a ${112}^{\ensuremath{\circ}}$ reorientation of the spin easy axis. The low-symmetry crystal-field environment of ${\mathrm{Bi}}_{2}\mathrm{W}{\mathrm{O}}_{6}$ and magnetoelastic coupling on the magnetic dopant provide a route to spin control via an applied electric field.