Application Of Dc Field Research Articles

CYM and RGB colored electronic inks based on silica-coated organic pigments for full-color electrophoretic displays

Chromatic organic pigment–SiO2 composite particles with six different colors (CYM and RGB) were prepared by a modified sol–gel method. With the aid of a cationic polyelectrolyte, poly(diallyldimethylammoniumchloride), amorphous silica was coated onto the surface of organic pigments which was revealed by the variation of the zeta potential and average particle size, together with TEM images and EDX and XPS results. Because of the fine scattering properties of silica to visible light, the intensity of the reflectance peak increased significantly, which makes the composite particles more vivid than the organic pigments. The chromatic electrophoretic suspension was prepared by mixing Span 85 and the composite particles anchored with a self-made block copolymer PLMA-b-PDMAEMA in tetrachloroethylene. All the colored ink particles have similar zeta potentials and mobility of about 30 mV and 4–5 × 10−10 m2 V−1 s−1, respectively. White/color (CYM and RGB) dual-particle electronic ink containing PLMA-b-PDMAEMA treated pigment–SiO2 composite particles and TiO2 grafted with a polymer present excellent performance and quick response under an applied DC field of 0.15 V μm−1.

Magnetometer Design for Measuring Ultralow DC Magnetic Fields Using YBa2Cu3O7−x Superconductors

In the present work we examined a special sensor design using a YBa2Cu3O7−x superconductor as a sensing element for the detection of ultralow DC magnetic fields. The experimental results have shown that the sensor signal, which is the second harmonic signal generated by co-application of AC and DC fields to high-T c superconductors, varies linearly with the applied DC field even in the −0.5 Oe to 0.5 Oe range. The critical factors affecting the strength of the second harmonic signal, such as the frequency and amplitude of the AC field, the intergrain critical field H c1J , and the minimum field required for penetration through the entire specimen H ∗, were optimized. In this way we could detect DC magnetic fields as low as 1 nT.

Influence of surface‐conductivity nonuniformity on charge accumulation of GIS downsized model spacer under DC field application

AbstractWhen a DC voltage is applied to an insulating spacer, the electric field distribution around it is determined by the resistivity of the material. Consequently, charges are accumulated on the surface of the insulator, and its breakdown voltage may become low. In this paper, the charge density distribution of the insulator is measured. The measured data indicate that the surface conductance is the main factor in charge accumulation. Therefore, the conductivity of the insulator is also measured, and the influence of the surface conductivity on charge accumulation is examined both experimentally and by numerical computation. It is confirmed that nonuniformity of surface conductivity is responsible for charge accumulation and the conductivity of the insulator in atmospheric‐pressure SF6 is estimated to be $\sigma = 1 \times 10^{-18} \Omega^{-1}$. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 181(2): 29–36, 2012; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/eej.22272

Preparation of ZnO Thin Film by Electrophoretic Deposition(EPD)

The electrophoretic deposition(EPD) of ZnO nano-sized colloids is investigated by changing the colloid number concentration, applied force, and deposition time. The change of the colloid size in a suspension was examined by the different colloid number concentrations (N = 3.98 × 10 15 , N = 3.98 × 10 14 , and N = 3.98 × 10 13 ) with an increase of the deposition time and applied forces. Deposition behavior was investigated by changing the applied fields (from DC 5 V to 50 V) and the deposition time (5 min to 25 min). The surface microstructures of the as-deposited films were investigated by SEM. The dried films were sintered from 850℃ to 1,050℃ for 2 h and then the microstructures were also explored by SEM. The agglomeration rate was enhanced by increasing the colloid number concentration of colloids. Colloid number concentration in a suspension must be rapidly decreased at higher values of the electric field. ZnO nano-sized colloids had the highest zeta potential value of over -28 mV in methanol. A homogeneous microstructure was obtained at colloid number concentration of N = 3.98 × 10 13 , applied DC field of 5 V/cm and 15 min of deposition time at an electrode distance of 1.5 cm. Under these conditions, the deposited films were sintered at 850℃ and 1,050℃ for 2 h. The results show a typical pore-free surface morphology of a uniform thickness of 400 nm under these experimental conditions.

Ultra-low DC Magnetic Field Detection Using Ceramic Superconductors

In the present study, the linear behavior of the second harmonic signal generated by application of very low DC magnetic fields to the polycrystalline bulk high-Tc superconductors has been examined. The amplitude of AC field, Hac, intergranular first critical field, H1cJ, and minimum field required for the magnetization of specimen as a whole, H∗, were determined and a special coil design has been presented. The results reveal that the second harmonic signal varies linearly with the applied DC field in the −0.1 Oe to 0.1 Oe range. Additionally, detection of ultra-low DC fields as small as 5 nT has been achieved. Repeatability and reproducibility tests were performed and the resultant data have been found to be consistent. In the light of our study, a commercial magnetometer can be produced to be utilized in successful detection of very low magnetic fields.

Dielectric model of point charge defects in insulating paraelectric perovskites

Some point defects (i.e., oxygen vacancies) create deep trapping levels in the bandgap of the paraelectric phase ferroelectric crystals. Under applied DC field the traps release electrons via the Poole-Frenkel mechanism and become charged. The electric field of a point charge polarizes the crystal locally reducing its permittivity. In this paper a simple theory is proposed for calculating the DC field dependent apparent (measureable) permittivity of a paraelectric crystal with point charge defects. It is shown that the apparent permittivity of a paraelectric crystal may be sufficiently lower as compared with the defectless crystal. This reduction is in addition to the possible reduction of the apparent permittivity associated with the interfacial “dead” layers and strain.

Modified tunable dielectric properties by addition of MgO on BaZr 0.25Ti 0.75O 3 ceramics

Phase composition, microstructure and tunable dielectric properties of (1 − x)BaZr 0.25Ti 0.75O 3– xMgO (BZTM) composite ceramics fabricated by solid-state reaction were investigated. It was found Mg not only existed in the matrix as MgO, there was also trace amount of Mg 2+ ions dissolved in the BZT grains, which led to Curie temperature of the BZTM composites ceramics shifting to below −100 °C. Dielectric permittivity of the BZTM composite ceramics was reduced from thousands to hundreds by manipulating the content of MgO. Johnson's phenomenological equation based on Devonshire's theory was used to describe the nonlinear dielectric permittivity of the ceramics with increasing applied DC field. With increasing content of MgO, anharmonic constant α ( T) increased monotonously. Dielectric permittivity was 672, while dielectric tunability was as high as 30.0% at 30 kV/cm and dielectric loss was around 0.0016 for the 0.6BaZr 0.25Ti 0.75O 3–0.4MgO sample at 10 kHz and room temperature.

Huge dielectric constant of Rb2CdI4 and K2ZnI4 crystals grown by Czochralski method

Temperature and frequency dependences of the dielectric constant and the spontaneous polarization were measured for crystals of Rb2CdI4 and K2ZnI4 obtained by the Czochralski method. The dielectric constant of both crystals shows a huge sharp peak just below the Curie point T C and the peak value is 57,000 at T C = 210.3 K of Rb2CdI4 and 27,000 at T C = 272.5 K of K2ZnI4. Below T C, it shows a shoulder-like dielectric dispersion, which is connected to ferroelectric domain motions. The spontaneous polarization of K2ZnI4 was measured by the pyroelectric method and is about 3.9 × 10–2 C m−2 at 4 K. The effects of dc field application on the dielectric properties are also discussed.

Dilution-Induced Slow Magnetic Relaxation and Anomalous Hysteresis in Trigonal Prismatic Dysprosium(III) and Uranium(III) Complexes

Magnetically dilute samples of complexes Dy(H(2)BPz(Me2)(2))(3) (1) and U(H(2)BPz(2))(3) (3) were prepared through cocrystallization with diamagnetic Y(H(2)BPz(Me2)(2))(3) (2) and Y(H(2)BPz(2))(3). Alternating current (ac) susceptibility measurements performed on these samples reveal magnetic relaxation behavior drastically different from their concentrated counterparts. For concentrated 1, slow magnetic relaxation is not observed under zero or applied dc fields of several hundred Oersteds. However, a 1:65 (Dy:Y) molar dilution results in a nonzero out-of-phase component to the magnetic susceptibility under zero applied dc field, characteristic of a single-molecule magnet. The highest dilution of 3 (1:90, U:Y) yields a relaxation barrier U(eff) = 16 cm(-1), double that of the concentrated sample. These combined results highlight the impact of intermolecular interactions in mononuclear single-molecule magnets possessing a highly anisotropic metal center. Finally, dilution elucidates the previously observed secondary relaxation process for concentrated 3. This process is slowed down drastically upon a 1:1 molar dilution, leading to butterfly magnetic hysteresis at temperatures as high as 3 K. The disappearance of this process for higher dilutions reveals it to be relaxation dictated by short-range intermolecular interactions, and it stands as the first direct example of an intermolecular relaxation process competing with single-molecule-based slow magnetic relaxation.

Mechanisms Limiting the Performance of ${\rm MgB}_{2}$ Polycrystalline Thin Film Microwave Resonators

We investigate the nonlinear behavior of magnesium diboride (MgB2) coplanar waveguide resonators in order to identify the basic mechanisms limiting the performance of polycrystalline MgB2 films in microwave applications. In particular, we focus on several kinds of switching response. Switching is observed due to increase of rf currents above a given threshold or to application of dc fields. In the former case a thermic model is able to account for the observed behaviors, including the presence of a thermal bistability regime. In the latter case, penetration of vortices at low fields is demonstrated and the effects of thermo-magnetic instabilities at higher fields are described.

An Investigation into the Effects of Substrate Temperature on Magnetic Properties of RF Sputtered NiFe Films

The paper describes results of investigation on sputtered NiFe Films to determine the sputter deposition condition that could produce magnetic field sensors with the desired magnetic properties. The magnetic materials used in such devices should have a low coercive force, a low anisotropy field and a low magnetization dispersion, α50. .The results of systematic investigation of radio-frequency (RF) sputtered, RF biased, 82-18 % NiFe films showed (i) Improved Kobelev methods were applied to magneto-optic measurement techniques, suppress the magnetization ripples when subjected under the application of dc field. (ii) Anisotropy field results indicated an inverse trend with increasing substrate temperature (iii) the experimental measurements on magnetization dispersion relatively constant up to 200 °C with α50 approximately 1.2°, it then increases more sharply to about 3.5° at 400 °C substrate temperature. The work also provide understanding of the effects on the magnetic properties of sputtered magnetic films that is very limited as current literature is almost entirely limited to evaporated magnetic films.

Electromechanical and light tunable cholesteric liquid crystals

A light-responsive cholesteric liquid crystal (CLC) mixture is tuned with light and applied DC electric field. Interestingly, the reflection of the CLC is red shifted with UV light and blue shifted with applied DC electric fields. UV light exposure induces a red shift in the reflection of the CLC bandgap by as much as 800 nm from the original spectral position. Spatial variations in pitch (and thus reflection color) are shown to blue shift with applied DC field regardless of the photohistory and restore the notch position or image upon removal of the field. The ability to tune the reflection of the CLC bandgap on demand to the red or blue with multiple stimuli is a never before demonstrated effect that could have potential utility in lasing, optical filtering, or data communication applications.

Single molecule magnet behaviour in robust dysprosium–biradical complexes

A Dy-biradical complex was synthesized and characterized down to very low temperature. ac magnetic measurements reveal single molecule magnet behaviour visible without any application of dc field. The transition to the quantum tunneling regime is evidenced. Photophysical and EPR measurements provide evidence of the excellent stability of these complexes in solution.

Second and Third Peaks in the Non-resonant Microwave Absorption Spectra of Superconducting Bi2212 Crystals

Non-resonant microwave absorption (NMA) measurements at liquid nitrogen temperature with systematic microwave power variation showed a two-peak structure in the Bi-2212 textured crystals, similar to that observed in the Bi-2212 single crystals (Srinivasu et al., in J. Supercond. Incorp. Nov. Magn. 14:41, 2001). NMA signals from the aged Bi-2212 single crystals show an emergence of a ‘third peak’ as a function of microwave power. We qualitatively interpret these second and third peaks as due to the microwave power induced phase locking of several number of junctions into coherent groups and then the destruction of the phase locking by the applied DC field leading to decoupling or fluxon motion, which gives the loss in individual junctions belonging to these otherwise coherent groups.

Granularity and Linear Flux Dynamics in Sintered LaO0.92F0.08FeAs

The flux dynamics in LaO0.92F0.08FeAs polycrystalline samples has been investigated looking at the first and higher harmonics of the AC magnetic susceptibility. The investigation of the real and imaginary part of the first harmonic shows that the critical temperature is reduced when the applied DC field increases. Moreover, the intergrain and intragrain contributions persist up to the highest applied DC field, suggesting that the electromagnetic connection among the superconducting grains is strong in spite of the estimated very short coherence length. Concerning the higher harmonics, a comparison between the absolute value of the real part of the first harmonic and the sum of the higher harmonics clearly indicates the activation of a linear regime below the superconducting critical temperature. Furthermore, the temperature range where this linear regime is activated is smaller than the one found in cuprate perovskite superconductors.

Dielectric properties and energy storage density in ZnO-doped Ba 0.3Sr 0.7TiO 3 ceramics

ZnO additions to Ba 0.3Sr 0.7TiO 3 ceramics have been studied in order to determine the role of this dopant on dielectric property and energy storage density development. The temperature and frequency dependences of dielectric constant, the breakdown strength, and the dielectric dissipation were measured. The dependence of dielectric constant to applied DC field was used to evaluate the energy storage densities. The crystalline structure and morphology were also investigated by XRD and SEM, respectively. Experimental results show that the stored energy density for the sample with 1.6 wt% ZnO addition is the highest among all the compositions. At 40 kV mm −1 electric fieled, its stored energy density can reach 3.9 J cm −3. Moreover, the ceramic with this composition has higher dielectric constant and breakdown strength, lower loss and dependency characteristic of dielectric constant to applied electric field.

Frequency- and axial-field-dependent circular magnetization reversal in a stress-annealed Fe-based nanocrystalline wire

Absract After suitable annealing under a tensile stress, Fe73.5Cu1Nb3Si13.5B9 amorphous wire becomes the nano-structured material together with a transverse anisotropy field Hk=−3.2 kA/m. Its circular permeability, μ=μ′−jμ″, was determined from the measurements of the impedance, as a function of the frequency (f=333–33,333 Hz) and amplitude (IAC=0.1–100 mA) of AC current and the axially applied DC field (H=0–89 kA/m). We found that the circular technical magnetization of this sample carried out by the spontaneous domain nucleation process. The influences of the AC current frequency and the axial DC field on the circular magnetization have been studied.

Investigation of Transient Processes in Nematic Liquid Crystal Cells with Semiconductor Substrate, Caused by the Electric Field Applied to Semiconductor

In the present work the results of detailed researches on characteristics of transient processes, appearing by application of DC field to semiconductor substrate of liquid crystal cell have been carried out. It is shown, that oscillations, caused by longitudinal DC field applied to the semiconductor differ from the oscillations, caused by the Freedericksz transitions. The dependences of character and number of these oscillations on the applied DC field value, the type and thickness of nematic liquid crystal are investigated. The probable mechanisms explaining the observable phenomena are discussed.

Vortex melting line and anisotropy of aBa2Ca3Cu4O8(O1−yFy)2 multilayered superconductor

We have measured the vortex melting lines of high-pressure-synthesizedBa2Ca3Cu4O8(O1−yFy)2 (nominalcomposition, 2y = 1.3, 1.6and 2.0) F(2y)-0234multilayered high-Tc superconductor using fundamental and third harmonic susceptibility responsescarried out on preferentially oriented crystallites with very low ac field amplitude(5 µT) and in applied dc fields up to 6 T. The vortex melting lines of all three F-substitutedsamples show interesting doping dependence and are very well described by the commonlyaccepted theory of melting lines. Interestingly, we discovered that the models describing thetemperature dependence of the in-plane London penetration depth also dependon the doping level: the 3D XY model for the nearly-optimum-doped sample[F(1.3)], the mean-field theory for the under-doped sample [F(1.6)] and the two-fluidmodel for the heavily-under-doped sample [F(2.0)]. We found that the vortexmelting lines in F-0234 are determined by the interplay in the coupling of pancakevortices through the charge reservoir layer (CRL), and through the block of innerCuO2 planes (IPs), respectively. The anisotropy values (47 for the near-optimally-doped sample)derived from experimental vortex melting lines are consistent with the values obtained byfirst-principles electronic-band-structure calculations.

Vortex melting line and dimensional crossover in Ba2Can−1CunO2n(O1−y,Fy)2 cuprate superconductors

Ba2Can−1CunO2n(O1−y,Fy)2[F(2y)-02(n−1)n], homologous series with F-substitution at apical oxygen site possess a thinner, 7.4Å, charge reservoir layer (CRL) and a strong interlayer vortex coupling was expected in these systems. We measured the vortex melting lines of high pressure synthesized Ba2Ca3Cu4O8(O1−yFy)2 (2y=2.0) multilayered system with 2 inner planes (IP) of CuO2 layers and Ba2Ca1Cu2O4(O1−yFy)2 (2y=1.4, 1.6 and 2.0) bilayer system with no IP; using fundamental and third harmonic susceptibility response carried out onto preferentially oriented crystallites at very low ac field amplitude and applied dc fields up to 12T. These experimental melting lines are described by the commonly accepted theory of two-fluid model. We observed 3D to 2D crossover in heavily underdoped F(2.0)-0212 sample, whereas such a vortex lattice crossover is not evident in F(2.0)-0234 sample; and explained on the basis of heavily underdoped and self doped states.