Change Of External Field Research Articles

Magnetism and magnetocaloric effect in multicomponent Laves-phase compounds: Study and comparative analysis

This paper presents a review and results of comparative study of the influence of Gd on some physical properties of (R0.9R′0.1)1−xGdxCo2 solid solutions with R=Dy, Ho and R′=Er, Ho and x varied from 0.05 to 0.15. Powder X-ray diffraction analysis performed at room temperature revealed that all studied solid solutions solidify with the formation of a Laves-phase MgCu2-type structure (space group Fd−3m). The magnetization behavior and the magnetic transition are analyzed in terms of the Landau theory. The studies of magnetic properties and heat capacity showed that a relatively small Gd addition significantly increases TC of the compounds. The maximum percentage increase in TC, namely, ~43% was observed for (Ho0.9Er0.1)1−xGdxCo2. However, the highest temperature was noted for the (Dy0.9Ho0.1)0.85Gd0.15Co2 solid solution; it is TC=183.4K. Below the ordering temperature, all samples are ferrimagnetically ordered; at high temperatures, they are Curie–Weiss paramagnets. Moreover, a small Gd addition eliminates the field-induced magnetic transition near TC and, as consequence, transforms the nature of magnetic transition from the first- to second-order.The magnetocaloric effect has been estimated in terms of both isothermal magnetic entropy and adiabatic temperature changes. The highest adiabatic temperature change ΔTad=3K and highest isothermal entropy change ΔSmag=12.1J/kgK were observed for (Ho0.9Er0.1)0.95Gd0.05Co2 at ~90K in magnetic fields of 2T and 3T, respectively. A decrease in the entropy change has been observed with increasing Gd content in all studied samples. The smallest values of ΔSmag were observed for the (Dy0.9Ho0.1)1−xGdxCo2 solid solutions. Under an external field change of from 0 to 3T, the maximum entropy change for (Dy0.9Ho0.1)1−xGdxCo2 compounds decreases from 6.9at x=0.05–4.3J/kgK at x=0.15. The refrigerant capacity for all solid solutions (with 0.05≤x≤0.15) is reported. The effect of increasing Gd content in the solid solutions on their magnetic and magnetocaloric properties is discussed.

Effect of partial Gd substitution on the magnetic and magnetocaloric properties in Dy-Ho-Gd-Co multicomponent compounds

The magnetic and magnetocaloric properties of polycrystalline (Dy0.9Ho0.1)1−xGdxCo2 (0.0 ≤ x ≤ 0.15) solid solutions were investigated experimentally using magnetic measurements; the Landau theory was also applied to clarify peculiarities of the magnetic phase transition in the compounds. X-ray diffraction patterns taken at room temperature exhibit the existence of the C15 cubic Laves phase structure for all samples under study. The lattice parameter increased from 0.7186 for x = 0.0 to 0.7194 nm for x = 0.15 and the Curie temperature TC increases from 130 to 183 K as the Gd content increases to x = 0.15. The isothermal entropy change ΔSmag was calculated according to magnetic measurements using the thermodynamic Maxwell's relation. A decrease in entropy change with the increase of Gd content has been observed. Under an external field change of from 0 to 3 T, the maximum entropy change decreased from 8.1 for x = 0.0 to 4.3 J kg−1 K−1 for x = 0.15. The effect of increasing the Gd amount in the (Dy0.9Ho0.1)1−xGdxCo2 solid solutions on their magnetic and magnetocaloric properties is discussed.

Experimental study of the magnetocaloric effect in Dy1−xErxCo2 solid solutions doped with Gd

Magnetic and magnetocaloric properties of polycrystalline (Dy0.9Er0.1)1−xGdxCo2 (0.0 ⩽ x ⩽ 0.25) solid solutions were investigated experimentally using magnetic measurements. The magnetization behavior and magnetic transition are analyzed in terms of Landau theory. Powder X-ray diffraction analysis performed at room temperature showed that all (Dy0.9Er0.1)1−xGdxCo2 (0.0 ⩽ x ⩽ 0.25) solid solutions are C15 cubic Laves phase with the MgCu2-type structure. The lattice parameter increases from 0.7187 for Dy0.9Er0.1Co2 to 0.7204 nm for (Dy0.9Er0.1)0.75Gd0.25Co2. In this case, the Curie temperature increases from 128 K to 215 K for. At higher temperatures, all solid solutions are Curie–Weiss paramagnets. The isothermal entropy change −ΔSmag was calculated using magnetic measurements data and thermodynamic Maxwell’s relation. A decrease in the entropy change has been observed with increasing Gd content. Under an external field change of from 0 to 3 T, the maximum entropy change for these compounds decreases from 8.5 at x = 0.0 to 3.1 J/kg K at x = 0.25. The refrigerant capacity of the (Dy0.9Er0.1)1−xGdxCo2 solid solutions (with 0.0 ⩽ x ⩽ 0.25) is presented. The effect of increasing Gd content in the (Dy0.9Er0.1)1−xGdxCo2 solid solutions on their magnetic and magnetocaloric properties is discussed.

The analytical model of rheological fluid for vibration and noise control

Rheological fluids (RF) also known as a controllable viscosity fluids (CVF) introduced in the area of vibration control of mechanical systems made possible a more efficient control of both: transient and continuous vibration. They are also used in design of sound barriers to control noise transmission loss and diaphragms for modification of noise absorption characteristics of sound absorbing materials. Their apparent viscosity is controllable by the use of external (electrical in electro-rheological ER or electromagnetic in magneto-rheological MR fluids) field. In the absence of applied external field, the RF exhibits Newtonian-like behavior. Applied external field changes this behavior and the RF shows in addition a yield shear stress which depends on strength of this field. In proposed model, the shear stress is expressed as a superposition of two components. One of them is proportional to the viscosity and relative velocity of a base fluid, and the second one, which depends on strength of applied external field. Modification of external field strength according to selected design parameter (velocity or time or distance—combination of them) allows to develop family of vibration or sound attenuating devices, which were not achievable before.

Electrocaloric and electrostrictive effect of polar P(VDF–TrFE–CFE) terpolymers

The electrocaloric effect (ECE) is the adiabatic temperature change or isothermal entropy change caused by the polarization change of a dielectric material when subjected to a change of external electric field. The electrostrictive effect is a form of elastic deformation of a dielectric induced by an electric field, associated with those components of strain which are independent of reversal field direction. It was found that both the ECE, e.g., adiabatic temperature change, and the electrostrictive strain in poly(vinylidene fluoride–trifluoroethylene–chlorofluoroethylene) (P(VDF–TrFE–CFE)) terpolymers are proportional to the square of the electric field. The adiabatic temperature change ΔT of ECE versus electric field can be illustrated using a modified Belov–Goryaga equation. ΔT is proportional to E2 when E is small. For electrostrictive effect, the rigid-ion model assumes that the anharmonic movement of the ions leads to the quadratic strain–electric field relation. The quotient of electrostrictive coefficient Q over the phenomenological coefficient β is empirically a constant, indicating that the larger the electrostrictive coefficient, the larger the ECE, which opens a new way to find out new electrocaloric materials.

Effect of partial Ho-substitution on the magnetic and magnetocaloric properties of polycrystalline DyCo2-based solid solutions

Structural, magnetic and magnetocaloric properties and heat capacity of polycrystalline Dy1−xHoxCo2 (0.1⩽x⩽0.5) solid solutions were investigated experimentally using by X-ray diffraction, magnetic and heat capacity measurements; the Landau theory was applied also to clarify peculiarities of magnetic phase transition in the compounds.X-ray diffraction patterns taken at room temperature exhibit the existence of the C15 cubic Laves phase structure for all samples under study. The lattice parameter decreased from 0.7186 for x=0.1–0.7179nm for x=0.5 and the Curie temperature TC decreases from 130 to 109K as the Ho content increases to x=0.5. The isothermal entropy change −ΔSmag was calculated according to magnetic measurements using thermodynamic Maxwell’s relation. A large entropy change has been observed for all Ho concentrations. Under an external field change from 0 to 3T, the maximum entropy change fluctuates within 9J/kgK. The maximum ΔTad value varies within 3 and 2K for a magnetic field change of 2 and 1T, respectively. The effect of increasing Ho amount in the Dy1−xHoxCo2 solid solutions on their magnetic and magnetocaloric properties is discussed.

Effects of stress on the hysteresis loss and coercivity of ferromagnetic film

The JA-SW hybrid model is extended in order to include the strain or stress anisotropy. With this improved model, a simulation is carried out to study the effects of stress on magnetic hysteresis loss and coercivity of ferromagnetic film. It is shown that the hysteresis loss and coercivity are related to the external field orientation, the stress intensity and the stress direction. Hysteresis loss, or the coercive force does not entirely monotonially increase with the change of stress intensity. For example, when the external field is parallel to the easy axis, a valley appears in the curve. In addition, stress will cause the peak offset of the coercivity curve as the orientation angle of the external field changes. Extensive comparisons of results with literature data are made and the differences between them are explained.

Plasmonic modulator optimized by patterning of active layer and tuning permittivity

We study an ultra-compact plasmonic modulator that can be applied in photonic integrated circuits. The modulator is a metal–insulator–metal waveguide with an additional ultra-thin layer of indium tin oxide (ITO). Bias is applied to the multilayer core by means of metal plates that serve as electrodes. External field changes carrier density in the ultra-thin ITO layer, which influences the permittivity. The metal–insulator–metal system possesses a plasmon resonance, and it is strongly affected by changes in the permittivity of the active layer. We propose several optimizations to improve performance of the structure. We examine influence of the ITO permittivity on the modulator's performance and point out appropriate values. We analyze eigenmodes of the waveguide structure and specify the range for its efficient operation. We show that substituting the continuous active layer by one-dimension periodic stripes increases transmittance through the device and keeps the modulator's performance at the same level. The dependence on the pattern size and filling factor of the active material is analyzed and optimum parameters are found. Patterned ITO layers allow us to design a Bragg grating inside the waveguide. The grating can be turned on and off, thus modulating reflection from the structure. The considered structure with electrical control possesses a high performance and can efficiently work as a plasmonic component in nanophotonic architectures.

Magnetocaloric effect and transition order of Mn5Ge3 ribbons

Single phase Mn5Ge3 ribbons were successfully synthesized by single roller melt-spinning method followed by an annealing procedure at 800°C for 1h. The magnetocaloric effect and transition order were investigated by dc magnetization measurement. A maximum entropy change of 4.92J/kg K and a refrigerant capacity of 201.3J/kg were observed at an external field change of 30kOe. The Banerjee criterion was adopted to discriminate the order of the transition, indicating a second order transition. The calculated entropy changes were also obtained by Landau theory, which are in agreement with the experimental values at the temperature region above the Curie temperature. This phenomena implies a potential transition of the magnetic interaction in the vicinity of the Curie temperature. Universal behavior was also indicated in that all of the experimental entropy change curves collapse into one universal curve, which is consistent with the Banerjee criterion.

Nanospherical heterolayer in strong electrostatic field

The influence of a strong homogeneous electric field on the states of charge carriers in the structure of quantum dot–quantum well (QDQW) is studied theoretically. It is shown that a strong external field changes radically the character of carrier motion in the structure and leads to an additional field-localization of the particle along the polar angle variable. An explicit form of the wave functions and energy spectrum of single-particle states in the structure in the presence of an external field is obtained. The possibilities of experimental and operational applications of the theoretical results obtained for the study of core/layer/shell structures as well as of hollow spheres are also shown.

Full transient response of Taylor cones to a step change in electric field

We studied experimentally the complete transient response of Taylor cones subject to a step change in external electric field with the goal of finding optimal conditions to reduce the overall response time and achieve the highest possible switching bandwidth. The transient behavior of electrified menisci is of interest for many applications that would benefit from active control of on/off switching of the electrospray, such as femtoliter droplet-on-demand or novel fuel injectors in next generation internal combustion engines. We first investigated the transient behavior of ethanol, a typical solvent for droplet-on-demand. We then expanded the study to fuels such as JP-8 and E-30 biogas, a biofuel with 30% ethanol (vol.). The system response is a multi-stage process that can last from ~100 μs to ~100 ms. Potential bottleneck stages include liquid accumulation, meniscus oscillation, and cone relaxation, depending on the experimental conditions. A typical full response time is ~1 ms, and the shortest transient process observed is ~400 μs. For a given liquid, nozzle outer diameter (OD) and applied voltage are the two most important parameters to influence the full response time. Onset or near-onset voltage for the establishment of the cone jet often leads to a large number of oscillation cycles and should be avoided. Changes in conductivity and viscosity by less than a factor of 10 have negligible effects on the transient process. Using JP-8 or E-30 biogas, 90 μm OD nozzle with extractor, and flow rate of 0.4 mL/h, we can routinely achieve bandwidth of 1 kHz, corresponding to a full response time of 1 ms, after which quasi-monodispersed droplets of ~10 μm are generated. Adaptation of an inviscid model of a charged oscillating droplet to the oscillating meniscus satisfactorily explains several key phenomena observed in our experiments, such as the full response time and the overshoot of the meniscus height.

Phase transition of nanotube-confined water driven by electric field

The effects of electric field on the phase behaviors of water encapsulated in a thick single-walled carbon nanotube (SWCNT) (diameter = 1.2 nm) have been studied by performing extensive molecular dynamics simulations at atmospheric pressure. We found that liquid water can freeze continuously into either pentagonal or helical solidlike ice nanotube in SWCNT, depending on the strengths of the external electric field applied along the tube axis. Remarkably, the helical one is new ice phase which was not observed previously in the same size of SWCNT in the absence of electric field. Furthermore, a discontinuous solid-solid phase transition is observed between pentagonal and helical ice nanotubes as the strengths of the external electric field changes. The mechanism of electric-field-induced phase transition is discussed. The dependence of ice structures on the chiralities of SWCNTs is also investigated. Finally, we present a phase diagram of confined water in the electric field-temperature plane.

Special themed issue on “Responsive gels”

This issue of Colloid and Polymer Science is devoted to the continually expanding field of responsive gels. While solvent-swollen polymer networks have been a topic of interest for many decades, networks that are able to respond to environmental cues such as changes in temperature, pH or other external fields have led to completely new lines of research. In this volume, the editors have attempted to capture a snapshot of the current state of the field, which, while focused on a specific type of material, is impressive in its intellectual breadth. Responsive gels have shown themselves to be outstanding model systems that allow researchers to probe fundamental aspects of soft matter. Those fundamental studies have, in turn, permitted responsive gels to be employed in a variety of different applications. This themed issue reflects the various directions of this very active research area. Most of the contributions from Germany are part of the Priority Programme SPP 1259 “Intelligent Hydrogels” funded by the Deutsche Forschungsgemeinschaft since 2006. Their continued commitment to this discipline is reflective of the continued vibrancy of the research. Beyond Germany, this issue contains contributions from five other countries; the field of responsive gels is clearly an international one. A notable characteristic of the field are its sub-divisions related to the length-scales and dimensionalities of the materials. Thus, this special issue presents work covering all aspects of stimuli-responsive macroscopic gels, as well as investigations of micro/nanogels and thin films. New synthetic approaches are addressed as well as physicochemical aspects and theoretical models. We sincerely hope you enjoy this special issue, and through it, gain an appreciation for both the scope and depth of the work produced by the responsive gels community. G. Sadowski and the editors of Colloid and Polymer Science

Effect of electrical field on crystallization and ferroelectric properties of Ge:Sb:Te films

AbstractIn this work impedance spectroscopy has been used to investigate of the NaCl type‐hexagonal transition in stoichiometric Ge2Sb2Te5 and in non‐stoichiometric (Ge24Sb15Te61) films. The temperature dependence of capacitance in all films shows an abrupt change (about 4‐6 times) at the temperature corresponding to the end of the NaCl type‐hexagonal transition. Additional, impedance measurements were carried out in films which have been crystallized with an external DC electric field. Comparing the results in the films crystallized with and without the external electric field, it is observed that in films crystallized with an external electric field, the capacitance increases during the NaCl type‐hexagonal transition for about 9‐15 times and that the piezoresponse force microscopy measurements have shown ferroelectric domains in the NaCl type phase. External electrical field changes significantly the onset of amorphous‐NaCl type crystallization temperature which could be related with an increase in atomic diffusion, promoting the growth of the crystalline phase. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Interpolation of externally-caused magnetic fields over large sparse arrays using Spherical Elementary Current Systems

Abstract. A physically-based technique for interpolating external magnetic field disturbances across large spatial areas can be achieved with the Spherical Elementary Current System (SECS) method using data from ground-based magnetic observatories. The SECS method represents complex electrical current systems as a simple set of equivalent currents placed at a specific height in the ionosphere. The magnetic field recorded at observatories can be used to invert for the electrical currents, which can subsequently be employed to interpolate or extrapolate the magnetic field across a large area. We show that, in addition to the ionospheric currents, inverting for induced subsurface current systems can result in strong improvements to the estimate of the interpolated magnetic field. We investigate the application of the SECS method at mid- to high geomagnetic latitudes using a series of observatory networks to test the performance of the external field interpolation over large distances. We demonstrate that relatively few observatories are required to produce an estimate that is better than either assuming no external field change or interpolation using latitudinal weighting of data from two other observatories.

Domains and Domain Walls in Multiferroic Ferroelectric-Ferromagnet and Control of Its Modulation

Ferroelectric-ferromagnet with inhomogeneous exchange-relativistic magneto-electric interaction (Dzyaloshinskii-Moriya) is studied theoretically in external electric field. The domain wall combines properties of usual 180° one in ferroelectric and unusual magnetic one, consisting of linear topological defects (Bloch lines), situated periodically with large density. It is shown that the external electric field changes both ferroelectric and ferromagnetic subsystems. It is found that the helicoids step is formed in each domain in the magnetic subsystem and Bloch lines period demonstrates incommensurate structure. Final solution for magnetic moment in Bloch lines and modulated helicoids period near domain wall can be expressed in Jacobian elliptic functions.

Refrigerant capacity and direct measurements of the magnetocaloric effect on LaFe11.2Co0.7Si1.1Cx materials

In this paper, we report on the magnetic properties and magnetocaloric effect (MCE) in NaZn13-type LaFe11.2Co0.7Si1.1Cx (x=0.1 and 0.3) close to room temperature. The Landau theory as well as the temperature dependence of magnetization data revealed that LaFe11.2Co0.7Si1.1C0.1 and LaFe11.2Co0.7Si1.1C0.3 exhibit a second-order magnetic transition near their Curie temperature. We have calculated the magnetocaloric effect both in terms of isothermal entropy change and adiabatic temperature change using the magnetization and the direct measurements. Under an external field change from 0 to 5 T, −ΔS is 14.5 J/kg K (TC=290 K) and 8 J/kg K (TC=310 K) for x=0.1 and 0.3, respectively. The calculated refrigerant capacity for a field change in 0–5 T is about 305 and 286 J/kg K, for LaFe11.2Co0.7Si1.1C0.1 and LaFe11.2Co0.7Si1.1C0.3 respectively, which is larger than that of some magnetocaloric materials with a first-order phase transition (Gd5Ge2Si2). ΔTad decreases with increasing C content. It was found to be about 1.5 for x=0.1 and 1.2 for x=0.3 under 1.48 T.

Tunable magnetocaloric effect around hydrogen liquefaction temperature in Tb 1−xY xCoC 2 compounds

The magnetic properties and magnetocaloric effect of Tb 1− x Y x CoC 2 ( x=0, 0.1, 0.2, 0.3, 0.4) compounds have been investigated systematically. All the compounds undergo second-order transitions from paramagnetic to ferromagnetic states without thermal and magnetic hysteresis. With increasing Y content from 0 to 0.4, the Curie temperatures decrease nearly linearly from 28 to 18 K. The nature of the second-order phase transitions can be confirmed by Arrott plots. For Tb 0.6Y 0.4CoC 2 compound, the maximum value of the magnetic entropy change –Δ S M at 20 K is 9.35 J kg −1 K −1 for an external field change of 5 T (5.14 J kg −1 K −1 for 2 T). The large reversible magnetic entropy change makes Tb 0.6Y 0.4CoC 2 compound an attractive candidate for the application at hydrogen liquefaction temperature.

Quanta Energy Level Structure and the First-Order Freedericksz Transition of Weak Anchoring NLC Cells

The energy problem of weak anchoring nematic liquid crystal (NLC) cell is investigated. For given system, there are four solutions satisfying mechanical equilibrium conditions simultaneity under certain condition. Liquid crystal system exist quanta energy level. The values and sequence of energy levels related to the change of external field and anchoring parameters. The state with the smallest energy is the stable state and the others are metastable states, which are separated by the energy barriers. The Freedericksz transition can be considered as the director slippage through these barriers to the lowest energy level and the first order transition and bistable state result from the existence of the multiple disturbed solutions.

鉛直直流電界中における燃料液滴の燃焼挙動に及ぼす電極間隔の影響(熱工学,内燃機関,動力など)

Flame is affected by external electric field because it contains ions and electrons related to chemical reaction. On the other hand, movement of ions and electrons affects external electric field due to their charge. Since there are a few studies to discuss the change of external electric field, this paper discusses the change of electric field from the experimental results with different electrode distance. It is supposed from 1-D steady-state analysis that if electric field is changed spatially the effect of electric field on combustion behavior is aligned with V^2/L^3 where V is applied voltage between electrodes and L is distance between the electrodes. Because flame deforms to cathode due to electric body force in electric field, the change of flame shape of burning ethanol droplet is observed in vertical DC electric field and electric current during combustion is measured. The result shows there exists the applied electric voltage where flame becomes vertically symmetry to balance the buoyancy by the electric body force and relation between m and n of V^m/L^n for flame symmetry is n/m=1.5. Depending on this result, it is proved that all experimental results with different electrode distance are aligned well with εV^2/L^3 which is a representing electric body force and the change of electric field due to the existence of flame can be estimated by brief 1D steady-state analysis.