Hysteresis Switching Research Articles

Electrical and Energy Storage Performance of Eu‐Doped PbZrO3 Thin Films with Different Gradient Sequences

The Eu‐doped compositionally graded multilayer PbZrO3 antiferroelectric thin films have been deposited on Pt(111)/Ti/SiO2/Si substrates by a sol–gel method. The effect of gradient sequence on microstructure, electrical properties, and energy storage performance has been investigated in detail. X‐ray diffraction patterns confirm that both thin films have crystallized into a unique perovskite phase. Down‐graded thin films have bigger grain sizes than up‐graded films, which is attributed to the influence of the gradient sequence of the thin films layer. The dielectric constant of down‐graded films is found to be higher than that of up‐graded films. Compared with up‐graded thin films, the energy storage density of down‐graded films is enhanced due to double hysteresis loop with small hysteresis switch, and high polarization.

Optimal Management and Differential Games in the Presence of Threshold Effects - The Shallow Lake Model

Abstract: In this article we analyze how the presence of thresholds influences multi agent decision making situations. We introduce a class of discounted autonomous optimal control problems with threshold effects and discuss tools to analyze these problems. Later, using these results we investigate two types of threshold effects; namely, simple and hysteresis switching, in the canonical model of the shallow lake. We solve the optimal management and open loop Nash equilibrium solutions for the shallow lake model with threshold effects. We establish a bifurcation analysis of the optimal vector field. Further, we observe that modeling with threshold effects simplifies this analysis. To be precise, the bifurcation scenarios rely on simple rules (inequalities) which can be verified easily. However, the qualitative behavior of the switching vector field is similar to the smooth case.

Anomalous magnetization reversal due to proximity effect of antiphase boundaries

Here we report anomalous double switching hysteresis loop and high coercivity ($\ensuremath{\sim}$0.1 T) in Fe${}_{3}$O${}_{4}$(110) thin films. Our analytical model based on spin chains confined within small antiphase boundary domains (APBDs) suggests a significant proximity effect of antiferromagnetic antiphase boundaries (APBs). Furthermore, the calculated domain size ($D$) follows the well-known scaling relation $D=C\sqrt{t}.$ The results suggest that the interface exchange coupling between neighboring magnetic domains through antiferromagnetic APBs is responsible for the double switching hysteresis. Our findings could help advance the studies of anomalous properties of magnetic materials originating from growth defects. This effect can be utilized for the tunability of exchange bias in devices.

Decentralized supervisory based switching control for uncertain multivariable plants with variable input–output pairing

In this paper, the design of decentralized switching control for uncertain multivariable plants is considered. In the proposed strategy, the uncertainty region is divided into smaller regions with a nominal model and specific control structure. The underlying design is based on the quantitative feedback theory (QFT). It is assumed that a MIMO-QFT controller exists for robust stability and performance of the individual uncertain sets. The proposed control structure is made up by these local decentralized controllers, which commute among themselves in accordance with the decision of a high level decision maker called the supervisor. The supervisor makes the decision by comparing the local models’ behaviors with the one of the plant and selects the controller corresponding to the best fitted model. A hysteresis switching logic is used to slow down the switching to guarantee the overall closed loop stability. It is shown that this strategy provides a stable and robust adaptive controller to deal with complex multivariable plants with input–output pairing changes during the plant operation, which can facilitate the development of a reconfigurable decentralized control. Also, the multirealization technique is used to implement a family of controllers to achieve bumpless transfer. Simulation results are employed to show the effectiveness of the proposed method.

Micromagnetic simulation of spin-transfer switching in a full-Heusler Co2FeAl0.5Si0.5 alloy spin-valve nanopillar

We investigated the spin-transfer switching in a full-Heusler Co2FeAl0.5Si0.5 alloy spin-valve nanopillar through micromagnetic simulation. A two-step switching hysteresis loop due to the fourfold in-plane magnetocrystalline anisotropy of Co2FeAl0.5Si0.5 layers was obtained. The simulation explains the experimental result of the resistance versus current hysteresis loop and yields good agreement with the measured critical current. Furthermore, the magnetization trajectory and magnetization distribution were shown and analyzed to elucidate the different characters of two-step switching.

Nonlinear stationary ac response of the magnetization of uniaxial superparamagnetic nanoparticles

The nonlinear stationary ac response of the magnetization of assemblies consisting of (i) noninteracting uniaxial superparamagnetic nanoparticles with aligned easy axes and (ii) randomly oriented nanoparticles subjected to superimposed ac and dc bias magnetic fields of arbitrary strength and orientation is calculated by averaging Gilbert’s equation augmented by a random field. The magnetization dynamics of uniaxial particles driven by a strong ac field applied at an angle to the easy axis of the particle (so that the axial symmetry is broken) alters drastically leading to new nonlinear effects due to coupling of the thermally activated magnetization reversal mode with the precessional modes via the driving ac field. In particular, the high frequency response reveals significant nonlinear effects in the precessional motion with significant consequences for the dynamic hysteresis and ultra-fast switching of the magnetization following an ultrafast change in the applied field.

A Simple Method to Reduce Torque Ripple in Direct Torque-Controlled Permanent-Magnet Synchronous Motor by Using Vectors With Variable Amplitude and Angle

In this paper, a modified direct torque control (DTC) for permanent-magnet synchronous machines, which enables important torque- and flux-ripple reduction by using voltage vectors with variable amplitude and angle, is proposed. In the proposed DTC, the amplitudes of torque and flux errors are differentiated and employed to regulate the amplitude and angle of the output voltage vectors online, which are finally synthesized by space-vector modulation (SVM). Two simple formulas are developed to derive the amplitude and angle of the commanding voltage vectors from the errors of torque and flux only. The conventional switching table and hysteresis controllers are eliminated, and a fixed switching frequency is obtained with the help of SVM. Stator flux is estimated from an improved voltage model, which is based on a low-pass filter with compensations of the amplitude and phase. The proposed DTC is comparatively investigated with the existing SVM-DTC from the aspects of theory analysis, computer simulation, and experimental validation. The simulation and experimental results prove that the proposed DTC is very simple and provides excellent steady-state response, quick dynamic performance, and strong robustness against external disturbance and control-parameter variations.

HYPERCHAOS IN A SPACECRAFT POWER SYSTEM

This paper presents some rigorous arguments on a chaotic strange attractor in a spacecraft power system, which is a 3D system with hysteresis switching. By carefully picking a suitable cross-section with respect to the attractor, we find a topological horseshoe of the corresponding third-returned Poincaré map, thus giving a rigorous verification of the existence of chaos in this system. Numerical computation shows that the two Lyapunov exponents of the Poincaré map are both positive and that there exists a two-directional expansion in this horseshoe, suggesting that this attractor is hyperchaotic in nature.

Enhanced Magnetic and Ferroelectric Properties and Current-Voltage Hysteresis by Addition of La and Ti to BiFeO3 on 0.7%Nb-SrTiO3

By adding La and Ti, we improve the magnetic and ferroelectric properties of Bi0.8La0.2Fe0.92Ti0.08O3 and Bi0.8La0.2FeO3 films on 0.7% Nb-SrTiO3. In Bi0.8La0.2Fe0.92Ti0.08O3 and Bi0.8La0.2FeO3, the saturation magnetization and the coercivity are several times higher than those in BiFeO3. The La and Ti additions reduce the leakage current, and increase the remnant electric polarization. A resistance switching is observed in Bi0.8La0.2Fe0.92Ti0.08O3/0.7%Nb-SrTiO3 and Bi0.8La0.2FeO3/0.7%Nb-SrTiO3 interfaces. Also, it is observed that Bi0.8La0.2Fe0.92Ti0.08O3/0.7%Nb-SrTiO3 has a wider current-voltage hysteresis and a larger resistance difference than Bi0.8La0.2FeO3/0.7%Nb-SrTiO3. In the interface of Bi0.8La0.2Fe0.92Ti0.08O3/0.7%Nb-SrTiO3, the ratio of high to low resistance is 103 and 105 times, at 300 K and 10 K, respectively. The voltage pulses can switch the resistance to vary in the 2 states. The transport mechanisms show that a trap-controlled space-charge-limited current induces current-voltage hysteresis and resistance switching. The current of Bi0.8La0.2Fe0.92Ti0.08O3/0.7%Nb-SrTiO3 decays with the Curie—Von Schweidler law.

Calculations on switching characteristics of ferroelectric–paraelectric superlattices

We study the switching characteristics of a superlattice consisting of a periodic ferroelectric and paraelectric layer with interlayer coupling using the Landau–Khalatnikov equation. The inhomogeneity of polarization at the ferroelectric or paraelectric surface is described by the extrapolation length δ. The effects of various parameters such as the viscosity coefficient, layer thickness, interlayer coupling and temperature on the switching characteristics are investigated. Our study shows that the hysteresis loop and switching current versus applied field depend strongly on those parameters. Interlayer coupling increases the ferroelectricity of the superlattice, leading to a strong enhancement in polarization and coercive field.

Magnetization configurations and reversal of magnetic nanotubes with opposite chiralities of the end domains

For thick soft magnetic nanotubes with an anisotropy axis directed along the nanotube length the equilibrium energy ground states present magnetization configurations with opposite rotating senses in two tube ends (B-state), referring as antiparallel chiralities of the end vortex domains. For nanotubes with outer radius R of 50 nm, 100 nm and 150 nm, and length L = (2.5–20)R the B-state remanent magnetization and the reversal field dependence on tube thickness and anisotropy strength are studied by using both two-dimensional simulation and analytic methods. The equilibrium states, the hysteresis loops and the switching field values calculated numerically are presented as the functions of tube size and material parameters. For the short nanotubes the domain walls patterns, such as transverse walls and vortex walls, nucleating in the tube center, as well as the hysteresis loops of the nanotubes with transverse walls are presented. The numerical results are interpreted by a simple analytical model in which the equilibrium state of nanotube is described by θ, the angle of the magnetization M deviation from the intrinsic tube easy axis. θ as a function of the tube aspect ratio L/R, tube thickness ΔR, and uniaxial anisotropy constant Ku, obtained by minimizing the total magnetic energy, well describes dependences of the shape of hysteresis loops and switching field values on the tube geometric and material parameters in the B-state.

DYNAMICS IN TIME-DELAY RECURRENTLY COUPLED OSCILLATORS

A model of time-delay recurrently coupled spatially segregated neural oscillators is proposed. Each of the oscillators describes the dynamics of average activities of excitatory and inhibitory populations of neurons. Bifurcation analysis shows the richness of the dynamical behaviors in a biophysically plausible parameter region. We find oscillatory multi-stability, hysteresis, and stability switches of the rest state provoked by the time delay as well as the strength of the connections between the oscillators. Then we derive the equation describing the flow on the center manifold that enables us to determine the bifurcation direction and stability of bifurcated periodic solutions and equilibria. We also give some numerical simulations to support our main results.

ELECTRIC, MAGNETIC AND MECHANICAL COUPLING EFFECTS ON FERROELECTRIC PROPERTIES AND SURFACE POTENTIAL OF BiFeO3 THIN FILM

BiFeO 3 (BFO) is usually considered as a multiferroic material, which shows both ferroelectric and antiferromagnetic properties at room temperature. It is an important material having potential applications in various spintronics devices. Many studies have been done to understand the ferroelectric and magnetic responses of BFO; therefore, this work is focused on characterizing the coupling effects of electric, magnetic and mechanical field on the ferroelectric properties and surface potential of the BFO thin films. A polycrystalline BFO film (~200 nm) is deposited on the Si substrate by the Pulse Laser Deposition techniques. The Vertical Piezoresponse Force Microscopy (PFM) is used to study the ferroelectric domain structure and the hysteresis loop of as-deposited BFO film as well as the effects of the mechanical stress and magnetic field on those properties. Kelvin Probe Force Microscopy (KPFM) is used to measure the surface potential of the samples. To apply the mechanical stress on the film, micro-indentations were made on the surface of the film with two different loads (1.96 N, 2.94 N). Then the ferroelectric domain structure, strain amplitude, domain switching (hysteresis response) behavior and surface potential are measured at the locations near the side of the indentation cavity and cracks. This way, the coupling effects of electric, magnetic and stress field on BFO film are studied at nanoscale.

Analytical vector generalization of the classical Stoner–Wohlfarth hysteron

In view of the difficulties in using the well-known Stoner–Wohlfarth (SW) ferromagneticsingle-domain particle as a vector hysteresis unit in statistical models of hysteresis like thePreisach-type model or in micromagnetic models, we propose a new description of thesingle-domain ferromagnetic grains by using a vector hysteron (VH) as the 2D and 3Dgeneralization of the rectangular hysteron. The vector hysteron introduced from magneticsymmetry considerations describes analytically the properties of a range of single-domainferromagnetic particles and also provides the physical motivation for the linear form of theenergy barrier used in several dynamic models. In this paper we show the maincharacteristics of the analytical vector hysteron by comparing it with the well-knownStoner–Wohlfarth model. We compare the hysteresis curves, switching fields and energeticproperties of the uniaxial single-domain particles as provided by the two models.

Understanding electroforming in bipolar resistive switching oxides

We study electroforming on the resistive switching (RS) behavior of silver-manganite interfaces. Using the technique of hysteresis switching loops we define an electroforming procedure that enables us to study its influence on the RS behavior in a systematic manner. We show that two similar electroforming procedures may lead to either RS or no RS at all. We explain the observed behavior by associating the forming procedure and the memory switching operation to major and minor hysteresis loops, respectively. With the obtained insight we propose a simple and nearly optimal electroforming procedure.

Polarization Reversal Kinetics in Strontium Barium Niobate Relaxor Crystals

The domain nucleation and growth during the switching process in ferroelectric relaxor Sr0.61Ba0.39Nb2O6 single crystals have been observed by means of nematic liquid crystal (NLC) method. Microscale studies of switching process in conjunction with electrical measurements allowed us to establish a relationship between local properties of domain dynamics and macroscopic response i.e., polarization hysteresis loop and switching currents. For the interpretation of experimental data we utilized two alternative theories concerning the domain growth: the Kolmogorov-Avrami-Ishibashi (KAI model) that involves nucleation and unrestricted growth of domains and nucleation—limited switching (NLS model) focused on the statistics of nucleation.

Manifestation of Structural Disorder in the Polarization Kinetics of Non-Uniform TAAP and Relaxor SBN Ferroelectric Crystals

The comparative experimental analysis of the polarization reversal kinetics in non-uniform Te(OH)62NH4H2PO4(NH4)2HPO4 (TAAP) and relaxor Sr0.61Ba0.39Nb2O6 (SBN:61) crystals have been performed. Micro-scale studies of domain switching in conjunction with electrical measurements allowed us to establish a relationship between local properties of domain dynamics and macroscopic response; polarization hysteresis loop and switching currents. We investigated the microscopic features of 180 degree domain walls dynamics and relate its dynamics to the defect structure in both type of the crystals. The domain structure was studied by means of the nematic liquid crystal decoration method.

Sliding mode control of uncertain switched delay systems via hysteresis switching strategy

This paper investigates the robust sliding mode control (SMC) problem for a class of uncertain switched systems with time-varying delay. The sliding surface is constructed such that the sliding motion is completely invariant to all admissible uncertainties. For the case of the known delay-derivative upper bound, by using the multiple Lyapunov functions method, the Hysteresis switching law dependent on the state and the previous value of switching signal are designed to stabilize the sliding motion and avoid the chattering. Variable structure controllers are developed to drive the state of switched systems to reach the sliding surface in finite time and remain on it thereafter. For the case of the unknown delay-derivative upper bound, based on the single Lyapunov function method, the conditions of stabilization are obtained. Finally, a numerical example is given to illustrate the effectiveness of the proposed methods.

Electrowetting on Paper for Electronic Paper Display

The use of paper as a material for various device applications (such as microfluidics and energy storage) is very attractive given its flexibility, versatility, and low cost. Here we demonstrate that electrowetting (EW) devices can be readily fabricated on paper substrates. Several categories of paper have been investigated for this purpose, with the surface coating, roughness, thickness, and water uptake, among the most important properties. The critical parameter for EW devices is the water contact angle (CA) change with applied voltage. EW devices on paper exhibit characteristics very close to those of conventional EW devices on glass substrates. This includes a large CA change in oil ambient (90-95°), negligible hysteresis (∼2°), and fast switching times of ∼20 ms. These results indicate the promise of low-cost paper-based EW devices for video rate flexible e-paper on paper.

Magnetization configurations and reversal of thin magnetic nanotubes with uniaxial anisotropy

We present calculations of the magnetization configuration and reversal behavior of magnetic nanotubes with uniaxial anisotropy by means of two-dimensional micromagnetic simulations and analytical methods. The tube radii R from 50 to 150 nm and the tube length /radius aspect ratio L/R≤20 were explored. For a finite length of magnetic nanotubes the magnetization configuration is characterized by a uniformly magnetized along the tube axis middle part and two nonuniform curling states of a length Lc in two ends of the tube with the same or opposite magnetization rotating senses, referring as C-state or B-state, respectively. We found that the magnetization configuration of the C-state exists for thin nanotubes with the tube thickness, ΔR, in the range of ΔR/R≤0.2. For thicker nanotubes the strong magnetostatic stray field forces the change of rotating senses of the end domains in opposite directions (the B-state). The transition from the C-state to a vortex state with in-plane magnetization is described as function of the tube geometrical parameters. The nanotube hysteresis loops and switching fields were calculated. The simple analytical model was developed to describe the nanotube magnetization reversal reducing its description to the Stoner–Wohlfarth model with effective parameters. The equilibrium state of nanotube is described in terms of θ, the angle of the magnetization deviation from the intrinsic tube easy axis. The L/R dependence of the C-state magnetization, the shape of hysteresis loops and the switching field values are described by a dependence of θ on L/R.