Width Of Hysteresis Loop Research Articles

Unique spin transition and wide thermal hysteresis loop for a cobalt(ii) compound with long alkyl chain

The cobalt(II) compounds with long alkyl chains, [Co(C12-terpy)(2)](BF(4))(2)·EtOH·0.5H(2)O(1·EtOH·0.5H(2)O) and [Co(C12-terpy)(2)](BF(4))(2) (1) was synthesized and characterized. The compound 1·EtOH·0.5H(2)O exhibits a "re-entrant spin crossover". The compound 1 exhibits the reentrant spin crossover and multi phase transitions with a wide thermal hysteresis loop.

Cooperative spin transition in a lipid layer like system

A novel iron(II) mononuclear spin transition complex [FeL(py)(2)] displays an abrupt spin transition around 225 K accompanied by a very wide thermal hysteresis loop (∼50 K) that spreads out over 100 K. Crystal structure analysis in both low-spin and high-spin states reveals a lipid layer-like arrangement of the complex molecules and provides insights into the spin switching mechanism.

Size effects upon phase transitions in vanadium oxide nanocomposites

A phenomenological model has been proposed for the formation of the major thermal hysteresis loop of optical parameters upon the semiconductor-metal phase transition in vanadium oxide nanocomposites. It has been demonstrated that the effects associated with the influence of nanocrystallite sizes on the phase transition temperature in an individual nanocrystallite, which is determined by the width of the elementary hysteresis loop and the position of the phase equilibrium temperature on the temperature scale, manifest themselves in the form of pronounced features in the loop shape. In particular, the size effects for VO2 polycrystalline films are observed in the formation of a trapezoidal shape of the optical thermal hysteresis loop with a wide lower base, whereas these effects for nanocomposites based on porous glasses with VO2 nanocrystals are revealed in the form of the optical hysteresis loop with a narrow lower base (wide upper base). The proposed model also explains the symmetric shape of the major hysteresis loop for vanadium oxide nanocomposites based on opals. The size effects in opal nanocomposites with strictly fixed sizes of pores and, therefore, nanocrystallite sizes manifest themselves in the form of well-defined steps in the heating and cooling branches of the major hysteresis loop.

Reliability and Storage Capacity: a Compromise Illustrated in the Two-Step Spin-Crossover System [Fe(bapbpy)(NCS)2

The design of bistable magnetic systems should enable the storage of information by manipulation of the spin degrees of freedom. However, such a strategy relies on the preparation of target objects, whose environment must be controlled to favor a hysteretic behavior. Here, we report the successful modeling of a highly cooperative two-step spin-crossover iron(II) compound, [Fe(bapbpy)(NCS)(2)]. The magnetic susceptibility measurements and low- and high-temperature hysteretic cycles reflect the presence of an intermediate phase, which controls the memory-storage capacity of this material. It is shown that the hysteresis loop widths can be traced theoretically by evaluating the electrostatic contributions between the transiting units. Despite the apparent reduction of intermolecular interactions upon cooling, it is suggested that the enhanced fluctuations of the Madelung field are responsible for the observed hysteresis width changes. This counterintuitive scenario makes the preparation of information storage devices an even more challenging task, where theoretical inspections are very insightful.

Optimal design of a new seismic passive protection device made in aluminium and steel

In recent years many techniques for the seismic control of structures have been developed. Among these, the metallic hysteretic devices are able to dissipate a great amount of the energy entering the building during a seismic event, thanks to a stable behavior under cyclic loads that produces a wide hysteresis loop. Steel shear panels are examples of elasto-plastic elements, which dissipate energy under a shear behavior. Generally such dampers are known to possess large energydissipation capacity relative to their size; they are cost-effective and are able to protect nonstructural elements too. Moreover, the shear panels may be easily installed and substituted in the structure. As disadvantage, this kind of energy dissipating devices can dissipate energy only after they sustain inelastic excursions. As a consequence they are ineffective for vibrations that produce interstory drifts smaller than the yielding drift of the device. To overcome this constraint, Rai and Wallace and Foti and Diaferio proposed shear panels made in aluminium alloys. In fact, these alloys are very ductile with a yielding limit lower than ordinary steel. Numerical and experimental researches have been developed on aluminium shear links. Foti and Nobile performed characterization and shaking-table tests on some aluminium shear panels showing instability phenomena and problems of the connections of the devices to the structure. The aim of the present note is to find out the optimum geometrical configuration of an aluminium-steel shear panel in order to dissipate a large amount of the seismic energy.

Nonmonotonic behavior of magnetoresistance, R(H) hysteresis, and low-temperature heat capacity of the BaPb0.75Bi0.25O3 superconductor in a magnetic field: Possible manifestations of phase separation

The transport properties (R(T) and R(H) dependences at various values of the transport current in magnetic fields up to 65 kOe) and low-temperature heat capacity in magnetic fields up to 90 kOe of the BaPb0.75Bi0.25O3 superconductor (TC ≈ 11.3 K) are investigated with the goal of clarifying the mechanisms determining the nonmonotonic behavior and hysteresis of its magnetoresistance R(H). The type of R(H) hysteretic dependences for BaPb0.75Bi0.25O3 is analogous to that observed in granular high-Tc superconductors (HTSCs); however, unlike classical HTSC systems, the field width of the magnetoresistance hysteresis loop for polycrystalline BaPb0.75Bi0.25O3 depends on the transport current. This means that although the mechanisms responsible for the magnetoresistance hysteresis (the influence of the magnetic flux trapped in superconducting regions on the effective field in Josephson interlayers) are identical in these objects, the transport current in BaPb0.75Bi0.25O3 may considerably affect the diamagnetic response of the superconductor. A considerable effect of transport current on the field in which the R(H) dependences have a peak and exhibit hysterestic properties is observed. Such a behavior can be adequately interpreted using the model of the spatially inhomogeneous superconductor-insulator state proposed by Gorbatsevich et al. [JETP Lett. 52, 95 (1990)]. The nonmonotonic dependence of quantity C/T (C is the heat capacity) on the magnetic field discovered in the present study also agrees with the conclusions based on this model.

Hysteresis of Freedericksz transition in confined light beams

The effect of the transverse confinement of an incident light beam on the hysteresis of light-induced Freedericksz transition in a nematic liquid crystal cell is considered. The thresholds of the orientational instability of the director with an increase and decrease in the light beam’s intensity are calculated numerically in relation to its transverse size. The hysteresis loop width is shown to change nonmonotonically with an increase in the transverse dimension. In contrast to a homogeneous light beam, the hysteresis existence region is determined not only by the parameter (K3 − K1)/K3 but also by the parameter K2/K3. With an increase in the transverse beam size, the critical values of the parameter (K3 − K1)/K3 increase, while those of the parameter K2/K3 decrease.

Low Temperature Deposition of Ferromagnetic Ni-Mn-Ga Thin Films From Two Different Targets via rf Magnetron Sputtering

AbstractLow temperature (400°C) deposition of ferromagnetic Ni-Mn-Ga thin films is successfully performed via rf magnetron sputtering technique using co-deposition of two targets Ni50Mn50 and Ni50Ga50 on sapphire (0001) and Si (100) substrates. The films are in part amorphous with significant degree of crystallinity. The obtained crystallographic structure is shown to be substrate-dependent. Films on both substrates are ferromagnetic at room temperature (Curie temperature ∼ 332.5K) with well-defined hysteresis loops, low coercivity (∼ 100 Oe) and a saturation magnetization of ∼ 200 emu/cc. At low temperature (5 K), both films show increased magnetization value with wider hysteresis loops having higher coercivity and remanent magnetization. The process is therefore effective in achieving the appropriate thermodynamic conditions to deposit thin films of the Ni-Mn-Ga austenitic phase (highly magnetic at room temperature) at relatively low substrate temperature without the need for post-deposition annealing or further thermal treatment, which is prerequisite for the device fabrication.

The influence of surface chemical dynamics on electrical and optical properties of ZnOnanowire field effect transistors

We demonstrate the effect of surface chemical dynamics on carrier transport andrecombination processes of electron–hole pairs in ZnO nanowire field effect transistors. Wehave found that the electrical conductance decreases and the threshold voltages shift in apositive gate voltage direction, as electrical characteristics are measured repeatedly. Weassociate this with the enhancement of oxygen adsorption by capturing electrons from theinduced current during the probing. This results in an overall depletion of electrons andthus causes the positive shift in threshold voltages associated with the originand width of characteristic hysteresis loops. In addition, the surface environmentdependence of the photo-response related to a recombination process in ZnOnanowires is discussed in terms of the surface chemical reaction and band bending.

Recursive Memory-based Hysteresis Modeling for Solid-state Smart Actuators

This article presents a new modeling approach for the memory-dependent hysteresis phenomenon in a broad class of smart structures and systems. We propose a recursive formulation to relate the minor hysteresis trajectories to their surrounding loops. More specifically, each internal (minor) trajectory targets its previous turning point and converges to its neighboring loop with a tunable exponential rate. By applying the ‘curve alignment’ and the ‘wiping out’ properties at the turning points, we present a new strategy within the context of a memory-based hysteresis modeling framework. A Galfenol-driven micropositioning actuator and a piezoelectrically driven nanopositioning stage are used to experimentally validate the model. Galfenol exhibits large butterfly-type nonlinearity with a small hysteresis effect, while the piezoelectric actuator exhibits wide hysteresis loops. The model is able to precisely predict the major and minor hysteresis loops in both the Galfenol and piezoelectric actuators, and is expected to be effectively and conveniently applicable to general systems exhibiting memory-dependent hysteresis.

Experimental characterization and modeling of rate-dependent hysteresis of a piezoceramic actuator

Laboratory experiments were performed to characterize the rate-dependent hysteresis properties of a piezoceramic actuator under harmonic, complex harmonic and triangular excitations in the 0.1–500 Hz frequency range. The measured data were analyzed to describe the major and minor hysteresis loops as functions of frequency, magnitude and bias of the input voltage. The results revealed considerably larger hysteresis loop width and lower displacement response amplitude under frequencies above 10 Hz. A rate-dependent Prandtl–Ishlinskii model is developed for describing the rate-dependent hysteresis behaviour of the actuator. This model integrates rate-dependent play operator and density functions formulated on the basis of the rate of change of input and experimentally observed behaviors. The fundamental properties of the proposed rate-dependent play and stop hysteresis operators are also investigated. The model results attained under harmonic, complex harmonic and triangular inputs at different frequencies in the 0.1–500 Hz were compared with the corresponding experimental data to demonstrate model validity over the wide range of inputs. Very good agreements were observed between the model results and the measured data, irrespective of the type and frequency of excitation.

Effects of Metal Doping on the Spin-Crossover Properties of an Iron(II) Complex with Extended π-Conjugated Schiff-Base Ligand Having an N4O2 Donor Set

Abstract The spin-crossover (SCO) complex [Fe(qnal)2]·CH2Cl2 (1), (Hqnal: N-(8′-quinolyl)-2-hydroxy-1-naphthaldimine) with an N4O2 donor set, has been synthesized and characterized. Investigation of magnetic properties shows that the complex exhibits an abrupt and complete spin transition with a 5 K wide thermal hysteresis loop. The X-ray diffraction analysis of complex 1 reveals that the molecules are connected into a quasi one-dimensional chain through extended π–π interactions between aromatic rings of ligands. The effects of metal doping on SCO properties have been investigated in the mixed-metal system [Fe1−xMx(qnal)2]·CH2Cl2 (M = zinc(II) and nickel(II)). The results reveal that metal doping increases the gradual character of spin transition, and no marked differences found between zinc and nickel doping, which suggest the dominant effect of the doping-degree (concentration) rather than metal species on cooperativity. However, the metal doping shows different effects on critical temperature (T1/2), where a more pronounced descending of T1/2 is observed in response to increased Zn-doping than in Ni-doping, indicating the noticeable consequence of internal pressure due to the different radii of doping metal ions.

Mechanism of the hysteretic behavior of the magnetoresistance of granular HTSCs: The universal nature of the width of the magnetoresistance hysteresis loop

The hysteretic behavior of the magnetoresistance R(H) of granular high-temperature superconductors (HTSCs) of the Y-Ba-Cu-O, Bi-Ca-Sr-Cu-O, and La-Sr-Cu-O classical systems is investigated for transport current densities lower and higher than the critical density (at H = 0). All systems exhibit universal behavior of the width of the magnetoresistance hysteresis loop: independence of transport current under identical external conditions. This means that flux trapping in HTSC grains is the main mechanism controlling the hysteretic behavior of the magnetoresistance of granular HTSCs, while pinning of Josephson vortices in the intragranular medium makes no appreciable contribution to the formation of magnetoresistance hysteresis (when transport current flows through the sample). Experimental data on relaxation of residual resistance after the action of a magnetic field also confirm this conclusion.

Structure and Magnetic Properties of Iron(II/III) Complexes with N2O22– Coordinating Schiff Base Like Ligands (Eur. J. Inorg. Chem. 4/2009)

AbstractThe cover picture shows the general formula of the iron complexes presented in the Microreview by B. Weber and E.‐G. Jäger on p. 465ff with single crystals of one of the complexes in the background. The application of this system ranges over model compounds for biological systems to molecular magnets or molecular switches. The examples show the reversible binding of the biomolecule nitric oxide, a spin‐crossover complex with a 70 K wide thermal hysteresis loop around room temperature and an example for spontaneous magnetic ordering below 10 K.

Graphical Abstract: Eur. J. Inorg. Chem. 4/2009

AbstractThe cover picture shows the general formula of the iron complexes presented in the Microreview by B. Weber and E.‐G. Jäger on p. 465ff with single crystals of one of the complexes in the background. The application of this system ranges over model compounds for biological systems to molecular magnets or molecular switches. The examples show the reversible binding of the biomolecule nitric oxide, a spin‐crossover complex with a 70 K wide thermal hysteresis loop around room temperature and an example for spontaneous magnetic ordering below 10 K.

A “capacitor” model of the hysteresis of tunneling current in w-GaN/AlGaN(0001) structures

A “capacitor” model of the hysteresis is developed using the self-consistent calculation of the tunneling current in a w-GaN/AlGaN(0001) double-barrier structure. In the framework of this model, the current jumps and changes in the potential and the electric field in the structure upon transition from one branch of the current loop to the other branch are considered a result of the recharging of two joined capacitors with the plates located at the positions of the extrema of variations in the electron density in the regions of the emitter, the quantum well, and the collector. It is demonstrated that, when the external and internal fields in the quantum well compensate for each other, the tunneling current is sharply and irreducibly switched to the characteristics of the other resonance and forms a wide hysteresis loop so that, in the branches of this loop, the charge is redistributed between the quantum well and the collector. If the fields coincide with each other, there arises a narrow “singleresonance” hysteresis loop, which is accompanied by the transfer of the electron charge from the emitter to the collector. The developed model leads to agreement with the results of the self-consistent calculations and provides an illustrative interpretation of the complex electron tunneling processes.

Photoinduced Metal-to-Insulator Transition in a Manganite Thin Film

A persistent photoinduced metal-to-insulator transition has been confirmed in a manganite thin film, Pr_(0.55)(Ca_(0.75)Sr_(0.25))_(0.45)MnO3, near a multicritical point by monitoring with transport measurements and x-ray photoemission spectroscopy. Together with the previously reported reverse effect, the photoinduced insulator-to-metal transition, it is found that the relative stability of the metallic and insulating phases interchanges around 80 K in the middle of a very wide hysteresis loop, which is a manifestation of the large potential barrier due to the long-range elastic energy. It is shown that photons are much more effective in overcoming the barrier via the electronically excited intermediate states than via the heat mode.

Contact Angles, Pore Condensation, and Hysteresis: Insights from a Simple Molecular Model

We discuss the thermodynamics of adsorption of fluids in pores when the solid-fluid interactions lead to partial wetting of the pore walls, a situation encountered, for example, in water adsorption in porous carbons. Our discussion is based on calculations for a lattice gas model of a fluid in a slit pore treated via mean field density functional theory (MFDFT). We calculate contact angles for pore walls as a function of solid-fluid interaction parameter, alpha, in the model, using Young's equation and the interfacial tensions calculated in MFDFT. We consider adsorption and desorption in both infinite pores and in finite length pores in contact with the bulk. In the latter case, contact with the bulk can promote evaporation or condensation, thereby dramatically reducing the width of hysteresis loops. We show how the observed behavior changes with alpha. By using a value of alpha that yields a contact angle of about 85 degrees and maintaining the bulk fluid in a supersaturated vapor state on adsorption, we find an adsorption/desorption isotherm qualitatively similar to those for graphitized carbon black where pore condensation occurs at supersaturated bulk vapor states in the spaces between the primary particles of the adsorbent.

Research in hydraulic brake components and operational factors influencing the hysteresis losses

Up-to-date automotive brake systems place stringent requirements upon the performance, reliability, and active safety. Such advanced systems as antilock braking systems (ABS), the electronic stability programme system, and the anti-slip control system assist a driver in ensuring driving safety under many conditions. The influence of the brake components on active safety systems is mainly determined through the hysteresis loop width. Among other negative outcomes, this parameter limits the possible frequency of cyclic braking during ABS operation. This paper presents an experimental analysis of the factors influencing the hysteresis pressure losses in a hydraulic brake system. The factors under investigations are the brake pedal stroke velocity, the gaps between the brake pads and the brake disc, and the configuration of the brake system. Experiments were carried out on the brake test equipment at the Automotive Engineering Department, Faculty for Mechanical Engineering, Technische Universität Ilmenau, Germany.

Single-Laser-Shot-Induced Complete Bidirectional Spin Transition at Room Temperature in Single Crystals of (FeII(pyrazine)(Pt(CN)4))

Single crystals of the {Fe (II)(pyrazine)[Pt(CN) 4]} spin crossover complex were synthesized by a slow diffusion method. The crystals exhibit a thermal spin transition around room temperature (298 K), which is accompanied by a 14 K wide hysteresis loop. X-ray single-crystal analysis confirms that this compound crystallizes in the tetragonal P4/ mmm space group in both spin states. Within the thermal hysteresis region a complete bidirectional photoconversion was induced between the two phases (high spin right arrow over left arrow low spin) when a short single laser pulse (4 ns, 532 nm) was shined on the sample.