Direct Current Measurements Research Articles

Sensitive current measurement on a quantum antidot with a Corbino-type electrode

Quantum antidots (QAD), which are a potential energy hill in a quantum Hall state, offer an ideal test-bed to study bound states in quantum Hall states. So far, electron transport in QAD devices has been investigated mostly by measuring the voltage between voltage probes, which, however, may not be suitable to detect small current on the order of pico-amperes or less. Here, we utilize a Corbino-type electrode to directly measure the current through the QADs. We find the direct current measurement with a current–voltage converter provides a more precise tunneling current than the voltage measurement with a voltage amplifier.

Time-lapse monitoring of an electrokinetic soil remediation process through frequency-domain electrical measurements

The electrokinetic (EK) method is an emerging technique for soil remediation, even though a monitoring system of the contaminant removal through geophysical methods has not been developed yet. In this paper, frequency-domain time-lapse measurements are used on heavy-metal contaminated sediments for monitoring an EK remediation process in a small-scale measuring cell. Our goal is to monitor the development of the electrokinetic process within the sediment and to evaluate the total time needed for the treatment. In fact, frequency-domain electrical monitoring provides complex resistivity spectra at different time steps that can be correlated to changes in the physical properties of the sediments. We perform laboratory spectral induced polarization (SIP) measurements on different samples before, during and after the EK treatment, using different electrolyte solutions (acids and tap water), commonly employed in EK remediation. Direct-current measurements (resistivity and chargeability) were also acquired on one sample for testing the reliability of the system by a comparison with a widespread commercial instrumentation for field measurements.Results indicate that resistivity is a diagnostic parameter as long as it is linked to changes in water saturation, pH and ionic concentration and not to the percentage of metal extraction. The resistivity exhibited well-defined signatures as a function of time that changes depending on the conditioning agent and the grain size distribution. These peculiarities were used to understand the physical processes occurring within the cell and consequently to assess the effectiveness of the electrokinetic treatment.Conversely, the polarization effect was negligible using acids as conditioning agents at the electrolyte chambers. Therefore, the SIP method is not effective under these conditions, being the polarization effect significant only when tap water was used at both ends of the measuring cell. In this case, we were able to correlate changes in water saturation with the time-shift observed on relaxation time distributions (RTDs) after inversion of SIP data and to observe, using normalized chargeability, that polarization is stronger at high pH values.On these basis, resistivity is suitable to monitor the development of the remediation, to optimise the energy levels required for treatment and to assess the end time of the EK process (time when metal mobilization ends). In fact, the end time of treatment can be associated with the time at which resistivity becomes stable. This time is highly dependent on the particular working conditions and sediment grain size as demonstrated by our experiments.

Influence of Crystallographic Orientation on Schottky Barrier Formation in Gallium Oxide

Highly rectifying graphite/I²-Ga2O3 Schottky junctions have been prepared by a simple low-cost drop-casting process. The influence of two different crystal orientations on the current transport mechanism in the graphite-based Schottky junctions was investigated by direct-current (DC) and alternating-current (AC) electrical measurements. The nonideal behavior observed for both $$ \left\langle {\bar{2}01} \right\rangle $$ and $$ \left\langle {010} \right\rangle $$ crystallographic orientations can be explained by the lateral inhomogeneity of the junction related to the imperfection of the graphite/semiconductor interface. A lower density of interface states and their shorter time constants are reported for Schottky junctions formed on $$ \left\langle {\bar{2}01} \right\rangle $$ crystallographic plane, as reflected also by the higher effective barrier height and lower ideality factor.

Physical, Structural and Dielectric Parameters Evaluation of New Mg1-x Cox NiyFe2-yO4 nano-ferrites Synthesized via Wet Chemical Approach

Department of Chemistry, Institute of Natural Sciences, University of Gujrat, Gujrat 50700, Pakistan The surfactant assisted co-precipitation method has been used to synthesize the Co2+ and Ni2+ substituted magnesium nanoferrites. The Co2+ and Ni2+ ions substitute the Mg2+ and Fe3+ ions from the magnesium ferrites, respectively. To study the effect of substituted ion concentrations on the dielectric performance of the MgFe2O4 spinel ferrites. The substituted magnesium nanoferrites with the compositions Mg1-x Cox NiyFe2-yO4 (x, y = 0.0, 0.1, 0.2, 0.3, 0.4, and 0.5) were synthesized to notice the effect of substituted ions concentration on the dielectric properties. Thermogravimetric analysis of the precursor precipitates was taken to investigate the stable spinel phase formation temperature. The X-ray diffraction analysis of the all substituted samples confirms the successful formation of the stable spinel phase and also exposes the effects of substituted ions on the crystal structure and unit cell constants. The presence of a characteristic absorption band (400 cm−1, 550 cm−1) of spinel ferrites in the Fourier Transform Infra Red (FT-IR) spectrum of substituted magnesium nanoferrites also confirms the formation of desire phase. The effect of temperature on the conductivity of the all substituted samples was observed within the temperature range of 25°C–300°C by two-probe direct current electrical resistivity measurements. Dielectric measurements of the substituted magnesium nanoferrites were carried out to study their magnetic behavior. The inverse relation of the dielectric parameters of the all substituted magnesium nanoferrites with frequency shows their excellent potential for devices that operate at higher frequencies.Department of Chemistry, University of Okara, Renala Khurd, Okara, Pakistan Department of Chemistry, Allama Iqbal Open University, H-8, Islamabad 45320, Pakistan.

Elaboration and Characterization of Materials from the LaMnO3–BiMnO3 Binary System

The study of the La(1‐x)BixMnO3 system is conducted using X‐ray diffraction (XRD) and electrical measurements. A continuous solid solution is evidenced for the LaMnO3 rich part of this system (x ≤ 0.6). According to the analyses of XRD results, a rhombohedral symmetry () is observed for x ≤ 0.4 and a cubic structure for x = 0.5. The structural study allows to determine an increase in the mean perovskite lattice parameter, together with a decrease in the rhombohedral angle up to a cubic symmetry for x = 0.5. For x > 0.6, the system is no more single‐phased. Impedance measurements are conducted for ceramics in a wide‐frequency range (100 Hz–1 MHz), between room temperature and 800 °C. The exponential decrease in the alternative current (AC) conductivities (σAC) and the room temperature values correspond to a semiconducting behavior. Direct current (DC) conductivity measurements (σDC) are also performed below room temperature (25 K < T < 300 K). The results evidence for a metal–insulator phase transition. For the exponential part of the σDC curves, the gap energy is between 0.1 and 0.2 eV, confirming the semiconductor behavior of these materials.

Enhanced piezoelectric properties of Mn‐modified Bi5Ti3FeO15 for high‐temperature applications

AbstractBi5Ti3FeO15 (BTF) has recently attracted considerable interest as a typical multiferroic oxide, wherein ferroelectric and magnetic orders coexist. The ferroelectric order of BTF implies its piezoelectricity, because a ferroelectric must be a piezoelectric. However, no extensive studies have been carried out on the piezoelectric properties of BTF. Considering its high ferroelectric‐paraelectric phase transition temperature (Tc ~ 761°C), it is necessary to analyze the piezoelectricity and thermal stabilities of BTF, a promising high‐temperature piezoelectric material. In this study, lightly manganese‐modified BTF polycrystalline oxides are fabricated by substituting manganese ions into Fe3+ sites via the conventional solid‐state reaction method. X‐ray diffraction and Raman spectroscopy analyses reveal that the resultant manganese‐modified BTF has an Aurivillius‐type structure with m = 4, and that the substitutions of Fe by Mn lead to a distortion of BO6. The temperature‐dependent dielectric properties and direct‐current (DC) resistivity measurements indicate that the Mn ions can significantly reduce the dielectric loss tanδ and increase the DC resistivity. The piezoelectricity of BTF is confirmed by piezoelectric constant d33 measurements; it exhibits a piezoelectric constant d33 of 7 pC/N. Remarkably, BTF with 4 mol% of Mn (BTF‐4Mn) exhibits a large d33 of 23 pC/N, three times that of unmodified BTF, whereas the Curie temperature Tc is almost unchanged, ~765°C. The increased piezoelectric performance can be attributed to the crystal lattice distortion, decreased dielectric loss tanδ, and increased DC resistivity. Additionally, BTF‐4Mn exhibits good thermal stabilities of the electromechanical coupling characteristics, which demonstrates that manganese‐modified BTF oxides are promising materials for the use in high‐temperature piezoelectric sensors.

Detecting crack and damage location in self-sensing fiber reinforced cementitious composites

This paper investigated the feasibility of using direct current (DC) measurements for detecting the cracking and identifying the location of cracks in self-sensing fiber-reinforced cementitious composites (SS-FRCCs) based on the electrical response of SS-FRCCs. The electro-mechanical response of SS-FRCCs with three different types of specimens (with a cold joint, a double-edged notch, and two double-edged notches) under direct tension is investigated. The test results indicated that the location of the crack (one-crack or multi cracks or main crack opening) could be notably determined by measuring the electrical resistivity of SS-FRCCs using two or multi-channel DC measurements. Under direct tension, the SS-FRCCs produced a clear reduction in electrical resistivity of cracked zone, but not in that of the un-cracked zone. Moreover, the amount of reduction in the electrical resistivity of cracked zone decreased as the location of the crack was close to the inner electrode.

Emittance study of the high intensity highly charged heavy ion beams extracted from electron cyclotron resonance ion source

According to the requirements of ion beams extracted from an electron cyclotron resonance ion source transverse phase space coupling research and the afterglow beam property effective measurement, a pepper pot type meter called PEMiL (Pepper Pot Emittance Meter in Lanzhou) has been designed, fabricated, and commissioned to obtain the emittance of high intensity highly charged heavy ion beams. The direct current beam emittance measurement results verify the coupling property caused by the semisolenoid field. This paper also describes the scheme of multiple exposure accumulation which was applied to measure the afterglow beam property, and the transverse phase space distribution of the oxygen afterglow beam which was measured for the first time is presented.

Structural, Morphological and Electrical Properties of CdO Thin Film Produced by Sol–Gel Spin Coating Procedure

A sol–gel spin coating procedure was used to produce cadmium oxide (CdO) thin film on the precleaned glass substrate. The structural, morphological and electrical properties of the produced film were specified by XRD, SEM and two-probe method. The polycrystalline nature with cubical structure of the cadmium oxide (CdO) thin film was confirmed by X-ray diffraction (XRD). Scanning electron microscope (SEM) confirms the uniform formation of film. The semiconducting character of the film was confirmed by electrical conductivity (direct current) measurement in dark. The Hall effect measurement of cadmium oxide film confirms the n-type conductivity.

Metal–Ligand Ratio Controlled Assembly Of Two Heterometallic CuEr Cluster Complexes: Syntheses, Structures and Magnetism

Two new heterometallic CuEr cluster complexes based on 3,5-dichlorobenzoic acid (HL) and 2,2′:6′,2″-terpyridine (TPY), [Cu(L)(TPY)][Er(L)4]·H2O (1) and [Cu(L)(TPY)][Er2(L)7] (2), have been hydrothermally prepared by controlling the metal–ligand ratios. Comparative study revealed that metal–ligand ratios affected the coordination modes of L− and thus generate two distinct structures. Both complexes display as ion-pair bicomponent structures. The cationic [Cu(L)(TPY)]+ components show the similar binuclear cluster structure in two complexes, while the two anionic parts are very different. In 1, two Er(III) centers are coordinated by four bridging and four chelating L− ligands to form the binuclear anionic [Er2(L)8]2− cluster. While in 2, all L− ligands show the bridging modes and connect the Er(III) centers into an extended one-dimensional (1D) chain. So the overall structures of 1 and 2 are bicomponent 0D + 0D and 0D + 1D structures, respectively. Direct current magnetic susceptibility measurements were performed for two complexes and they both showed antiferromagnetic behavior.

High-Pressure Crystallographic and Magnetic Studies of Pseudo-D5h Symmetric Dy(III) and Ho(III) Single-Molecule Magnets.

Single-ion magnets based on lanthanide ions in pseudo-D5h symmetry have gained much attention in recent years as they are reported to possess a large blocking temperature and a large barrier for magnetization reversal. Magneto-structural correlations reveal that the axial O-Ln-O angle is an important parameter to control the barrier, and while it can be fine-tuned by chemical modification, an alternative would be to utilize hydrostatic pressure. Herein, we report the crystal structures and static magnetic properties of two air-stable isostructural lanthanide SIMs under applied pressures. The complexes exhibit pseudo-D5h symmetry around the Ln(III)-ion (Ln = Dy or Ho), which coordinates to five equatorial water molecules and two large neutral phosphonic diamide ligands along the axial direction. High-pressure single-crystal X-ray diffraction experiments revealed two phase-transitions and an increasing deviation from D5h-symmetry between ambient pressure and 3.6 GPa. High-pressure direct-current magnetic measurements of the Dy(III) compound showed large steps in the hysteresis loops near zero field, indicative of quantum tunneling of magnetization (QTM). These steps grow in size with increasing pressure, suggesting that QTM becomes progressively more active, which correlates well with the pressure-induced increased overall deviation from pseudo-D5h symmetry and decreasing axial O-Dy-O angle. A strong temperature dependence of the step size is seen at 0.3 GPa, which shows that the SMM character persists even at this pressure. To understand the origin of significant variation in the tunneling probability upon pressure, we performed a range of ab initio calculations based on the CASSCF/RASSI-SO/SINGLE_ANISO method on both Dy and Ho complexes. From the energies and magnetic anisotropy of the mJ sublevels, we find a complex variation of the energy barrier with pressure, and using a constructed geometrical parameter, R, taking into account changes in both bond angles and distances, we link the magnetic properties to the first coordination sphere of the molecules.

Purely Spectroscopic Determination of the Spin Hamiltonian Parameters in High-Spin Six-Coordinated Cobalt(II) Complexes with Large Zero-Field Splitting.

Accurate determination of the spin Hamiltonian parameters in transition-metal complexes with large zero-field splitting (ZFS) is an actual challenge in studying magnetic and spectroscopic properties of high-spin transition metal complexes. Recent critical papers have convincingly shown that previous determinations of these parameters, based only on the magnetic data, have low accuracy and reliability. A combination of X-band electron paramagnetic resonance (EPR) spectroscopy and SQUID magnetometry seems to be a more convincing and accurate approach. However, even in this case, the accuracy of the determination of the spin Hamiltonian parameters is strongly limited. In this work, we propose a purely spectroscopic approach, in which three complementary EPR spectroscopic techniques are used to unambiguously with high accuracy determine the spin Hamiltonian parameters for transition-metal complexes with S = 3/2. The applicability of this approach is demonstrated by analyzing the new quasi-octahedral high-spin Co(II) complex [Co(hfac)2(bpy)] (I). Along with the conventional X-band EPR spectroscopy, we also use such advanced techniques as multi-high-frequency EPR spectroscopy (MHF-EPR) and frequency-domain Fourier-transform THz-EPR (FD-FT THz-EPR). We demonstrate that the experimental data derived from the X-band and MHF-EPR EPR spectra allow determination of the g tensor (gx = 2.388, gy = 2.417, gz = 2.221) and the ZFS rhombicity parameter E/D = 0.158. The axial ZFS parameter D = 37.1 cm-1 is measured for I with the aid of FD-FT THZ-EPR spectroscopy, which is able to detect the high-energy EPR transition between the two Kramers doublets. CASSCF/NEVPT2 quantum-chemical calculations of magnetic parameters and magnetic direct current (dc) measurements are performed as well as testing options, and the results obtained in these ways are in good agreement with those derived using the proposed spectroscopic approach.

Novel Wood Resistance Measurement Method Reducing the Initial Transient Instabilities Arising in DC Methods Due to Polarization Effects

A novel method for measuring the electrical resistance in wood is presented. It is based on applying an Alternating Current (AC) to two electrodes rammed into the wood. The method reduces the transient time for value stabilization. In case of Direct Current (DC) resistance measurement methods, typically used in wood measurement, an initial transient exists, invalidating the measured value during an initial transient period. This measurement method uses an electronic circuit based on a relaxation oscillator where the wood automatically sets the oscillation frequency depending on its electrical resistance. Compared to other AC methods, this circuit greatly simplifies the measurement process, not requiring any previous analysis for wood AC frequency estimation. Experimental results for four different wood species showed that, in all cases, the transient response of the measured wood resistance is improved when compared to the DC resistance method, reducing the stabilization time from 10–12 min in DC measurements to almost zero for the novel measurement method. The deviation between the initial wood resistance measurement and the stable value resulted in a range between 0.2% and 5% with the proposed method, while a range between 6% and 10% was obtained when using the DC method. Moreover, the proposed circuit is able to detect changes in wood resistance produced by small variations in temperature and environmental relative humidity during continuous long term measurements. For repeatability analysis, it was verified that similar ambient conditions of temperature and relative humidity (variations lower than 1 °C and 1%, respectively) in different moments provided variations lower than 1.5%. The method can also be applied to other fiber materials affectd by polarization effects when an electrical current is applied into them.

Ocean surface current retrieval from space: The Sentinel-2 multispectral capabilities

The Sentinel-2 MultiSpectral Instrument (MSI) collects multiple spectral band images, corresponding to specific sensing wavelengths and spatial resolutions, i.e. 10 m, 20 m and 60 m, respectively. Images are collected one at the time with a given time-lag between observations. Under favorable conditions, spatio-temporal characteristics of propagating ocean surface waves can thus uniquely be retrieved. A method for surface current vector field reconstruction is then developed. Demonstrated over different deep ocean regions, the retrieved surface current fields well compare with medium-resolution ocean circulation model or derived-velocities from altimeter measurements. At finer scales, the surface wave-conservation law is recovered, with the associated relationship between current vorticity and wave-ray curvature. Over shallow water regions, the wave propagation properties well follow sea depth variations, consistent with ETOPO1 data. Finally, time-lag between detector bands can also be exploited to estimate speed and direction properties of detected surface wave breaking whitecaps. An analysis of velocity reconstruction errors further reveals that Sentinel-2 MSI inter-channel co-registration is realized with an accuracy better than 0.1 pixel. Overall, these results confirm very promising capabilities of optical imagery to provide direct surface current velocity measurements from space, over relatively large areas, O(100 km), with a spatial resolution down to O(1 km).

Zero-Field Slow Magnetic Relaxation and Hysteresis Loop in Four-Coordinate CoII Single-Ion Magnets with Strong Easy-Axis Anisotropy.

Two mononuclear tetrahedral Co(II) complexes (HNEt3)2[Co(L1)2]·H2O (1) and (Bu4N)2[Co(L2)2]·H2O (2) (H2L1 = N,N'-bis(p-toluenesulfony1)oxamide, H2L2 = N,N'-diphenyloxamide) have been synthesized, and their structures have been characterized by single-crystal X-ray diffraction. Both complexes adopt distorted tetrahedral coordination geometries surrounding the Co(II) center, which is ligated by two doubly deprotonated oxamide ligands oriented perpendicularly to each other. Their axial magnetic anisotropies were revealed by the direct current (dc) magnetic measurements, high-field and high-frequency electron paramagnetic resonance, and theoretical calculations. Both complexes display slow magnetic relaxation in the absence of an applied dc field. Upon the application of the 0.15 T dc field, the quantum tunneling of magnetization is efficiently suppressed. In addition, both complexes display hysteresis loops with different field sweep rates at 1.8 K, which is rarely observed for Co(II) single-ion magnets (SIMs).

New Discoveries on Electromagnetic Action and Signal Presentation in Magnetic Flux Leakage Testing

Based on the authors’ previous work of magnetic flux leakage (MFL) quantitative description and the research plan especially for the magnetic component of eddy current effect factor $$ B_{other} $$, further explorations for electromagnetic actions, magnetic and signal presentations in the defect in electromagnetic nondestructive testing (ENDT, such as direct current field measurement (DCFM), MFL and eddy current testing (ECT)) are continued here. Primarily, new discoveries indicate that the magnetic component of $$ B_{other} $$ is actually composed of the secondary magnetic field component of $$ \Delta B_{mfl} $$ which manifests as raised signal waves and volume current perturbation component of $$ \Delta B_{\Delta I} $$ which features as double peaked signals due to the departure or bypassing of the “volume current” in the defect. What’s more, the concrete expressions of magnetic components are deduced and given through Ampere’s (or the Ampere–Maxwell) law. Afterwards, the theory is well demonstrated and verified by means of finite element analysis for current density and magnetic flux density or MFL signals in typical quasi-static testing by DC magnetization for different specimens with defects. Additionally, suggestions for installation site of sensor elements in ENDT are also given. Finally, a unified evaluation standard for magnetic flux density is formed, which provides the basic theory or analysis principles for the ENDT techniques as well as research directions for precision defect detection and related applications.

Controlling of Differential Resistance of <i>p–n</i>-Junctions of Bipolar Transistor in Active Mode by Method of Impedance Spectroscopy

Controlling of parameters of manufactured transistors and interoperational controlling during their production are necessary conditions for production of competitive products of electronic industry. Traditionally for controlling of bipolar transistors the direct current measurements and registration of capacity-voltage characteristics are used. Carrying out measurements on alternating current in a wide interval of frequencies (20 Hz–30 MHz) will allow to obtain additional information on parameters of bipolar transistors. The purpose of the work is to show the possibilities of the method of impedance spectroscopy for controlling of differential resistance of p–n-junctions of the bipolar p–n–p-transistor in active mode.The KT814G p–n–p-transistor manufactured by JSC “INTEGRAL” was studied by the method of impedance spectroscopy. The values of differential electrical resistance and capacitance for base–emitter and base–collector p–n-junctions are defi at direct currents in base from 0.8 to 46 µA.The results of the work can be applied to elaboration of techniques of fi checking of discrete bipolar semiconductor devices.

Two Types of Hexanuclear Partial Tetracubane [Ni4Ln2] (Ln = Dy, Tb, Ho) Complexes of Thioether-Based Schiff Base Ligands: Synthesis, Structure, and Comparison of Magnetic Properties.

New Schiff base ligand H2L containing N2O4S donor atoms has been explored for its ability to provide complexes of selected 3d and 4f metal ions. Room temperature reaction of H2L with NiCl2·6H2O and Ln(NO3)3·5H2O in the presence of Et3N in MeCN-MeOH (2:1) medium resulted in [Ni4Ln2(L)2(μ-Cl)2(μ3-OH)4(H2O)6]Cl4·2H2O (where Ln = Dy3+ (1), Tb3+ (2), and Ho3+ (3) and H2L = 2-((2-(2-(2-hydroxy-3-methoxybenzylideneamino)ethylthio)ethylimino)methyl)-6-methoxyphenol). Use of Ni(SCN)2·4H2O during synthesis provided SCN- ions for bridging and terminal coordination in [Ni4Ln2(L)2(μ-NCS)2(μ3-OH)4(NCS)4(H2O)2]·xMeOH·yH2O (where Ln = Dy3+ (4), x = 2, y = 4; Tb3+ (5) and Ho3+ (6), x = 0, y = 14.1). All six complexes possess a hexanuclear defective tetracubane topology having exchangeable bridging groups. The study of direct current magnetic susceptibility measurements revealed that the Ni(II) ions are engaged in ferromagnetic interaction with the DyIII, TbIII, and HoIII ions and have significant magnetic anisotropy in all six complexes. Alternating current susceptibility measurements confirmed that both of the two types of compounds qualify as zero-field single-molecule magnets (SMMs), and the effective barrier for the reversal of the magnetic moment was found to be in the range Ueff = 23-31 K for 1-2 and 4-5, respectively. Detailed insight into the electronic structure and magnetic properties was calculated using DFT- and CASSCF-based analyses. The found isotropic exchange parameter (J) values are JNi-Ni = -4.7 cm-1 for 1 and JNi-Ni = +29.2 cm-1 for 4 and clearly indicate that the μ-NCS-bridge is a better candidate than μ-Cl for ferromagnetic exchange interactions. Out of the six complexes, only complex 5 displays TbIII centered emission peaks at 451 and 480 nm.

Symmetry breaking of in-plane anisotropic magnetoresistance with temperature in La-doped Sr2IrO4 films

Electron-doped $\mathrm{S}{\mathrm{r}}_{2}\mathrm{Ir}{\mathrm{O}}_{4}$ has been the subject of much recent attention because of its similarities with hole-doped $\mathrm{L}{\mathrm{a}}_{2}\mathrm{Cu}{\mathrm{O}}_{4}$. However, direct evidence of its superconductivity has not yet been observed, which has led to various unresolved issues related to this material. In this study, a 14-nm-thick La-doped $\mathrm{S}{\mathrm{r}}_{2}\mathrm{Ir}{\mathrm{O}}_{4}$ film was grown on a (001) $\mathrm{SrTi}{\mathrm{O}}_{3}$ substrate. We found that the fourfold component of the in-plane anisotropic magnetoresistance disappears and is replaced by a twofold symmetry as the temperature increases. Variable-temperature x-ray diffraction and spatially resolved optical second-harmonic generation experiments eliminate the possibility of crystal structural distortion. The temperature dependence of direct current magnetization measurements indicates that a change in the spin structure may account for the symmetry breaking, similar to the nematic ordering of iron-based and other superconductors. Remarkably, the transition temperature of the symmetry breaking is well consistent with the previously reported onset (50 K) of the low-energy gap in K-doped $\mathrm{S}{\mathrm{r}}_{2}\mathrm{Ir}{\mathrm{O}}_{4}$ observed by scanning tunneling spectroscopy. Our results provide a perspective on these materials that helps elucidate the nature of magnetic interactions and explores the expected superconductivity of iridates.

Enhanced Adsorptive Properties and Pseudocapacitance of Flexible Polyaniline-Activated Carbon Cloth Composites Synthesized Electrochemically in a Filter-Press Cell.

Electrochemical polymerization is known to be a suitable route to obtain conducting polymer-carbon composites uniformly covering the carbon support. In this work, we report the application of a filter-press electrochemical cell to polymerize polyaniline (PAni) on the surface of large-sized activated carbon cloth (ACC) by simple galvanostatic electropolymerization of an aniline-containing H2SO4 electrolyte. Flexible composites with different PAni loadings were synthesized by controlling the treatment time and characterized by means of Scanning Electron microscopy (SEM), X-Ray Photoelectron Spectroscopy (XPS), physical adsorption of gases, thermogravimetric analysis (TGA), cyclic voltammetry and direct current (DC) conductivity measurements. PAni grows first as a thin film mostly deposited inside ACC micro- and mesoporosity. At prolonged electropolymerization time, the amount of deposited PAni rises sharply to form a brittle and porous, thick coating of nanofibrous or nanowire-shaped structures. Composites with low-loading PAni thin films show enhanced specific capacitance, lower sheet resistance and faster adsorption kinetics of Acid Red 27. Instead, thick nanofibrous coatings have a deleterious effect, which is attributed to a dramatic decrease in the specific surface area caused by strong pore blockage and to the occurrence of contact electrical resistance. Our results demonstrate that mass-production restrictions often claimed for electropolymerization can be easily overcome.