DC Measurements Research Articles

Probing the Magnetization Relaxation Dynamics of Four-Coordinate Lanthanide(III) Complexes

The reaction of bulky trimethylsilylanilide (N-TMSA) ligand with various lanthanide salts led us to isolate unusual and unique four-coordinate monomeric Ln(III) complexes which are challenging to isolate and not surprisingly rare in the literature. The single crystal X-ray diffraction unveils that all the complexes are monomeric and isostructural with the general molecular formula of [Ln(N-TMSA)3(THF)] where Ln = Dy (1) or Yb (2). Both complexes are found to possess distorted tetrahedral geometry. For all the complexes, detailed dc and ac susceptibility measurements were performed and both 1 and 2 show frequency-dependent out-of-phase susceptibility signals only in the presence of an optimum external magnetic field. The experimental observations are well supported by theoretical calculations and developed magneto-structural correlation using the various model complexes.

Origins of observational errors in field sweep DC measurements for unidirectional magnetoresistance

Understanding the mechanisms of unidirectional magnetoresistance (UMR) has become an important topic for its potential application of a two-terminal spin–orbit torque device. Field sweep DC measurements have been proposed and adopted to measure the value of UMR instead of second harmonic measurements. In this paper, potential measurement errors in conventional DC measurements are investigated. Oersted field and field-like torque usually do not influence the measurement, but a large field-like torque was found to lead to an anisotropic magnetoresistance difference when the sample is not perfectly aligned with the external field. The existence of ordinary magnetoresistance was also found to contribute to a large background. In this paper, an alternative measurement method for UMR was proposed and demonstrated to address those issues related to previous DC measurements. Our work may broaden the understanding of the error sources of UMR measurements and provide a reliable DC measurement method for the characterization of UMR.

Alkali (Na, K) doped SnO2: An investigation on the role of microstructure on electricity generation of oxide based ceramic hydroelectric cells

Generation of green electricity using porous nanostructure is a novel idea towards sustainable unconventional source of energy. Inexpensive, portable, eco-friendly, and biodegradable Alkali (Na, K) doped tin oxide nano porous structured hydroelectric cells were prepared by solid-state technique. X-Ray diffraction and Fourier transform infrared spectroscopy analysis have been performed to confirm the phase formation of the samples. Field emission scanning electron microscopy was used to investigate surface morphology of all the samples. Mesoporosity of the samples was confirmed by Barrett‐Joyner‐Halenda technique. Two-inch diameter circular pellets were prepared to investigate hydroelectric properties and it was found that maximum output power of 61.5 mW delivered by 5 Mol% K doped SnO2 HEC. The observed electricity generation in doped SnO2 samples is more sustainable as compared to pure SnO2 HEC. Water molecules dissociation and ionic conduction of dissociated ions were further investigated by dielectric, dc conductivity measurements for all the samples in dry and wet states. Observed results show that Alkali element doped tin oxide nano porous structured hydroelectric cells may use as nonconvention source of energy.

Dielectric and Spin-Glass Magnetic Properties of the A-Site Columnar-Ordered Quadruple Perovskite Sm2CuMn(MnTi3)O12

Perovskite-type ABO3 oxides show a number of cation-ordered structures, which have significant effects on their properties. The rock-salt-type order is dominant for B cations, and the layered order for A cations. In this work, we prepared a new perovskite-type oxide, Sm2CuMn(MnTi3)O12, with a rare columnar A-site order using a high-pressure, high-temperature method at about 6 GPa and about 1700 K. Its crystal structure was studied with synchrotron powder X-ray diffraction. The compound crystallizes in space group P42/nmc (No. 137) at room temperature with a = 7.53477 Å and c = 7.69788 Å. The magnetic properties of the compound were studied with dc and ac magnetic susceptibility measurements and specific heat. Spin-glass (SG) magnetic properties were found with TSG = 7 K, while specific heat, in the form of Cp/T, showed a strong, very broad anomaly developing below 20 K and peaking at 4 K. The dielectric constant of Sm2CuMn(MnTi3)O12 was nearly frequency and temperature independent between 8 K and 200 K, with a value of about 50. Cu2+ doping drastically modified the magnetic and dielectric properties of Sm2CuMn(MnTi3)O12 in comparison with the parent compound Sm2MnMn(MnTi3)O12, which showed a long-range ferrimagnetic order at 34-40 K. The antisite disorder of Cu2+ and Mn2+ cations between square-planar and octahedral sites was responsible for the SG magnetic properties of Sm2CuMn(MnTi3)O12.

Unraveling the origin of the peculiar transition in the magnetically ordered phase of the Weyl semimetal Co3Sn2S2

Recent discovery of topologically non-trivial behavior in Co3Sn2S2 stimulated a notable interest in this itinerant ferromagnet (Tc = 174 K). The exact magnetic state remains ambiguous, with several reports indicating the existence of a second transition in the range 125 -- 130 K, with antiferromagnetic and glassy phases proposed to coexist with the ferromagnetic phase. Using detailed angle-dependent DC and AC magnetization measurements on large, high-quality single crystals we reveal a highly anisotropic behavior of both static and dynamic response of Co3Sn2S2. It is established that many observations related to sharp magnetization changes when B || c are influenced by the demagnetization factor of a sample. On the other hand, a genuine transition has been found at Tp = 128 K, with the magnetic response being strictly perpendicular to the c-axis and several orders of magnitude smaller than for B || c. Calculations using density-functional theory indicate that the ground state magnetic structure consist of magnetic moments canted away from the c-axis by a small angle (~ 1.5deg). We argue that the second transition originates from a small additional canting of moments within the kagome plane, with two equivalent orientations for each spin.

Current-induced zero-field domain wall depinning in cylindrical nanowires

Multi-segmented cylindrical nanowires have properties that make them attractive for high-density, high-speed logic and memory applications. Investigations of the current-induced domain wall motion in cylindrical nanowires have, so far, typically been conducted with a background magnetic field. However, if performed at zero external field, they would be much more viable for their use in prospective electronic devices. Here, we present an all-magneto electrical method to consistently pin domain walls in multi-segmented nanowires and induce their de-pinning using current pulses. The experiments were conducted with compositionally modulated three-segmented nickel/cobalt/nickel and two-segmented cobalt/nickel nanowires of 190 and 150 nm diameter, respectively, where the soft/hard magnetic texture has been fairly studied. We find that for the 3 segmented nanowire, the domain wall can be de-pinned independent of the polarity of the pulse, while for the 2 segmented nanowire the domain wall de-pins only for one polarity. Applying current pulses of 1 × 1012 A/m2, we use a pulse width of 22 ns to estimate a lower boundary for the domain wall speed of 634.54 m/s in cobalt. We study the resistive heating effect from the DC measurement current to find a temperature increase of no more than 2 °C after more than 20 h of tests.

Fabrication of 3D microstructures in glass by direct writing electrochemical discharge machining

ABSTRACT The formation of 3D copper-filled microstructures in glass using direct writing electrochemical discharge machining (ECDM) and electrodeposition techniques is presented. Single-row stainless steel tool electrodes having tip sizes of 150 µm were made by wire electrodischarge machining (W-EDM). Tool wear mechanism and the tip size correction of the worn-out tools were investigated. Significant tool wear was observed after 5 ECDM repetitions of the tool electrodes involving drilling and milling operations. Due to the high temperature generated in the ECDM process, there is significant erosion in the tool electrodes, and the tip heights of the electrodes became non-uniform. Thus, the single-row tool electrode became non-reusable in the ECDM process. Therefore, the electrochemical dissolution (ECD) method was used to correct the tip dimension and make the tool reusable for the ECDM process. After the ECD correction, the obtained tip size was close to the original size of 150 µm with <5% inter-tip size variation. Up to two-cycle of ECDM and ECD size correction was performed; thus, enhanced reusability of the single-row tool electrodes was demonstrated. The 3D structures were metallized using the copper electroplating method. DC measurement of the microstructures showed good electrical connectivity with an ohmic nature.

State Estimation Using SCADA and PMU Measurements for Networks Containing Classic HVDC Links

• Hybrid state estimation (HSE) algorithm based on SCADA and PMUs measurements for AC power systems with embedded classic high voltage direct current (HVDC) links. • AC and DC measurements are modeled independently as functions of AC and DC states, respectively. • AC and DC measurements (states) are processed (estimated) simultaneously. • Coupling of AC and DC states is expressed by a set of three nonlinear equality constraints. This paper proposes a hybrid state estimation (HSE) algorithm which employs conventional measurements received from supervisory control and data acquisition (SCADA) system and synchrophasors measured from phasor measurement units (PMUs) for AC power systems with embedded classic high voltage direct current (HVDC) links. DC measurements obtained from the HVDC link are assumed to be sampled at the same rate as AC measurements. Zero injections and AC/DC coupling equations are modeled as equality constraints. By applying the nonlinear weighted least squares (WLS) algorithm with equality constraints, the HSE calculates both AC and DC states simultaneously. The effectiveness of the proposed algorithm is verified by simulations on the IEEE standard 14 and 30 bus test systems. The test results reveal the benefits of the proposed approach in terms of estimation accuracy and convergence speed.

Design and implementation of high-precision voltage measurement system based on Kalman filter and automatic calibration technology

With the rapid development of science and technology, precision measurement is of increasing importance. In this paper, we discuss noise reduction and automatic calibration issues for a high-precision voltage measurement system that covers voltages from 0.1 µV to 300 V and a frequency range from 10 Hz to 300 kHz (including DC). First, a modified Kalman filter is proposed to reduce measurement noise. Then, a self-calibration circuit is constructed to eliminate the systematic errors in DC voltage (DCV) measurements. Finally, a wideband AC calibration model is developed to overcome the defects in AC voltage (ACV) measurements caused by AC characteristics. The measurement application demonstrates the effectiveness of the proposed methods----the designed voltage measurement system has a DCV measurement accuracy of better than 9 µV/V and a high ACV accuracy of 0.25 mV/V in the frequency range of 30 Hz to 30 kHz at an ambient temperature of 25 °C. In addition, the minimum DC measurement uncertainty obtained on the DCV 10 V range is 0.4 μV/V (type A) and the minimum AC measurement uncertainty obtained on the ACV 10 V range is 2 μV/V (type A).

Possible transition between charge density wave and Weyl semimetal phase in Y2Ir2O7

The subtle interplay of band topology and symmetry broken phase, induced by electron correlations, has immense contemporary relevance and potentially offers novel physical insights. Here, we demonstrate charge density wave (CDW) in bulk Y$_2$Ir$_2$O$_7$ for T < 10 K, and its transition to the Weyl semimetal (WSM) phase at higher temperatures. The CDW phase is evidenced by a) current induced nonlinear conductivity with negative differential resistance at low temperature, b) low frequency Debye like dielectric relaxation at low temperature with a large dielectric constant, and c) an anomaly in the temperature dependence of the thermal expansion coefficient. The WSM phase at higher temperature is confirmed by the DC and AC transport measurements which show an inductive response at low frequencies. More interestingly, we show that by reducing the crystallite size, the low temperature CDW phase can be eliminated leading to the restoration of the WSM phase.

AlScN-Based SAW Magnetic Field Sensor for Isolated Closed-Loop Hysteretic Current Control of Switched-Mode Power Converters

This letter uses a surface acoustic wave magnetic field sensor for measurement and closed-loop current control of the inductor current in a GaN-based dc-dc power converter. The sensor is based on aluminium scandium nitride thin films with relatively high Sc concentration of 32% and fabricated on low-cost 8-in silicon substrate, with a magnetostrictive FeCoSiB film on top of a SAW delay line. The device has dc and bidirectional current measurement capability (derived from the magnetic flux density around a current trace) and is operated electrically isolated above the current trace. With permanent magnets as magnetic bias, the setup has a usable bidirectional current range of ±5 A. A phase detector IC measures the phase shift between the 296 MHz, 19 dBm input, and 35 dB attenuated output signal of the delay line sensor. The active sensor area has a distance of 2.5 mm from the current trace. In a 1.2 mT bias, the sensor is operated with a sensitivity of 18.28°/mT and bipolar current range of up to ±5 A. The sensor signal is enhanced by an analog filter to compensate the over 1 µs delay from the delay line and readout circuit. Finally, the sensor is used as the input of an analog hysteretic current control loop. The closed-loop current control operation is demonstrated using a 48 V GaN-based half-bridge dc-dc converter with 16 kHz triangular inductor current.

Slow spin dynamics and quantum tunneling of magnetization in the dipolar antiferromagnet DyScO3

We present a comprehensive study of static and dynamic magnetic properties in the Ising-like dipolar antiferromagnet (AFM) DyScO$_3$\ by means of DC and AC magnetization measurements supported by classical Monte-Carlo calculations. Our AC-susceptibility data show that the magnetic dynamics exhibit a clear crossover from an Arrhenius-like regime to quantum tunneling of magnetization (QTM) at $T^* = 10$ K. Below $T_{\mathrm{N}} = 3.2$ K DyScO$_3$ orders in an antiferromagnetic $GxAy$-type magnetic structure and the magnetization dynamics slow down to the minute timescale. The low-temperature magnetization curves exhibit complex hysteretic behavior, which depends strongly on the magnetic field sweep rate. We demonstrate that the low-field anomalies on the magnetization curve are related to the metamagnetic transition, while the hysteresis at higher fields is induced by a strong magnetocaloric effect. Our theoretical calculations, which take into account dipolar interaction between Dy$^{3+}$ moments, reproduce essential features of the magnetic behavior of DyScO$_3$. We demonstrate that DyScO$_3$ represents a rare example of inorganic compound, which exhibits QTM at a single-ion level and magnetic order due to classical dipolar interaction.

Investigating the Correlation between the Microstructure and Electrical Properties of FeSbO4 Ceramics.

FeSbO4 powder was prepared using the solid-state reaction method in this work. Afterward, the dense and porous ceramics were obtained by sintering the pressed powder calcined at temperatures of 900 and 1000 °C for 4 h. Rietveld profile analysis of the X-ray powder diffraction data showed that FeSbO4 adopts the trirutile-type structure (space group P42/mnm, with a ≅ 4.63 Å and c ≅ 9.23 Å). SEM images showed that the powder calcined at 900 °C after being sintered at 1200 °C resulted in ceramics of higher crystallinity, larger grains, and consequently, low porosity. The dielectric properties were measured in the frequency range of 10−1 Hz–1 MHz as a function of temperature (25–250 °C). The real (σ′) and imaginary (σ″) parts of the complex conductivity increase with rising annealing temperature for both samples. The real conductivity in the AC region for 𝑓 = 100 kHz was and for the ceramic samples obtained from the powder calcined at 900 (C-900) and 1000 °C (C-1000), respectively. Furthermore, the dielectric constants (k′) measured at room temperature and were (C-900) and (C-1000), while the activation energies of the grain region were Ea = 0.53 eV and Ea = 0.49 eV, respectively. Similar activation energy (Ea = 0.52 eV and 0.49 eV) was also obtained by the brick-layer model and confirmed by the adjustment of activation energy by DC measurements which indicated an absence of the porosity influence on the parameter. Additionally, loss factor values were obtained to be equal to 3.8 (C-900) and 5.99 (C-1000) for measurements performed at 100 Hz, suggesting a contribution of the conductivity originated from the combination or accommodation of the pores in the grain boundary region. Our results prove that the microstructural factors that play a critical role in the electrical and dielectric properties are the average grain size and the porosity interspersed with the grain boundary region.

Rational Construction of Molecular Electron-Conducting Nanowires Encapsulated in a Proton-Conducting Matrix in a Charge Transfer Salt.

Insulated molecular wires have gained significant attention owing to their potential contribution in the fields of nanoelectronics and low-dimensional chemistry/physics. Based on molecular charge transfer salts, we demonstrate, for the first time, the rational construction of molecular electron-conducting wires encapsulated in a proton-conducting matrix, which possibly paves the way to ionoelectronics. As expected from the molecular structure of the newly designed complex anion (i.e., propeller-shaped structure with hydrogen-bonding sites at four edges), a three-dimensional hydrogen-bonded framework was constructed within the crystal, which contains a one-dimensional array of an electron donor, tetrathiafulvalene (TTF). From the single-crystal crystallographic and spectroscopic studies, it was clarified that the nonstoichiometric deprotonation of anions and partial oxidation of TTFs occur, whereas the anion is electronically inert. Moderate conductivities of electron and proton were confirmed by dc and ac conductivity measurements. In addition, the electronic isolation of TTF wires was confirmed by the magnetic susceptibility data.

Dielectric response and molecular dynamics of nanocomposites based on TEMPO-oxidized cellulose nanofibrils and polyvinyl acetate

• Two series of nanocomposites based on Polyvinyl-acetate incorporated with two different TEMPO-oxidized cellulose nanofibrils were investigated. • The activation energy and the strength parameters were interpreted. • Electrical conductivity were evaluated using DC measurements. • The comparison between the two sets of CNF showed that PVAc/CNF-5 min films were able to build a denser CNF network and hence the highest potential of filling effect than those of PVAc/CNF-2 h films. A series of polyvinyl acetate polymer matrices (PVAc) incorporated with two different TEMPO-oxidized cellulose nanofibrils (CNF with 5 min and 2 h of oxidation) were studied. These composites have proven to be suitable for use as ion battery separators. For this purpose, dielectric properties and electrical conductivity have been investigated using impedance spectroscopy in the frequency range from 10 2 to 10 6 Hz and over the temperature range, 200–350 K. The effects of CNF loading on the molecular motion and the charge transport mobility in PVAc polymer chains were studied. Calculation of the strength parameter for the α-relaxation process revealed a threshold value of 8 % in the volume fraction of filler. A comparative study of the two nanocomposites films showed that PVAc/CNF-5 min nanocomposites were able to build a denser CNF network and hence the highest potential of filling effect than those of PVAc/CNF-2 h films. According to our results, the volume fraction of 8 % of CNF-5 min is recommended for achieving the highest performing nanocomposite with potential applications.

Fission chamber data acquisition system for neutron flux measurements on the Mega-Amp Spherical Tokamak Upgrade.

Neutron flux measurements are important in fusion devices for both safety requirements and physics studies. A new system has been built for the Mega-Amp Spherical Tokamak Upgrade (MAST Upgrade) that provides neutron count, DC, and Campbell mode measurements for a 1 µs period at 1MHz. The acquisition system uses a Red Pitaya board to sample current from two fission chambers mounted on the side of the MAST-U vessel. The system-on-chip design of the Zynq-7020 on the Red Pitaya also allows a web server implementation using Flask for data retrieval and diagnostic configuration over the MAST Upgrade network.

Electro-Optic Sensor for Measuring Electrostatic Fields in the Frequency Domain

Precise measurements of electrostatic fields in harsh environments are required in fields ranging from particle accelerators to industrial installations. Many techniques disrupt the field distribution due to the presence of conductors. We present a fully dielectric sensor for very harsh environmental conditions, that exploits the Pockels effect manifested by electro-optic crystals. This system is designed to allow DC measurements to be performed in the frequency domain. The paper discusses an analytical model and simulations of the system, validated with experimental results. The working principle of the measurement technique is explained in detail along the known limitations and possible solutions to further increase the performance.

Research of metering scheme key techniques for medium and low voltage DC distribution network

DC power grid has received increasing attentions recently, and with it comes the demand for highly reliable and stable metering solutions. At present, in the DC distribution projects that have been implemented, some DC metering devices have been put into use. However, from the national and industrial level, there is no clear standard for the design of the metering scheme for the medium and low-voltage DC distribution network, and there is a situation of imperfect metering device configuration. Therefore, based on the analysis of DC metering devices, algorithms and location selection, this paper takes the Hangzhou Jiangdong flexible DC distribution network as an example to analyze the error distribution caused by metering algorithm selection and device configuration. In addition, the influence of harmonics on DC measurement is analyzed to provide the suggestions for DC measurement solutions. The analysis has been verified by MATLAB/Simulink, which provides references for DC metering standards.

Label-free, ultrasensitive and rapid detection of FDA-approved TBI specific UCHL1 biomarker in plasma using MWCNT-PPY nanocomposite as bio-electrical transducer: A step closer to point-of-care diagnosis of TBI

Traumatic Brain Injury (TBI), a major cause of mortality and neurological disability affecting people of all ages worldwide, remains a diagnostic and therapeutic challenge to date. Rapid, ultra-sensitive, selective, and wide-range detection of TBI biomarkers in easily accessible body fluids is an unmet clinical need. Considering this, in this work, we report the design and development of a facile, label-free, highly stable and sensitive, chemi-impedance-based sensing platform for rapid and wide range detection of Ubiquitin-carboxy terminal hydrolase L1 (UCHL1: FDA-approved TBI specific plasma biomarker), using carboxylic functionalized MWCNTs embedded polypyrrole (PPY) nanocomposites (PPY/f-MWCNT). The said nanocomposites were synthesized using chemical oxidative polymerization method. Herein, the functionalized MWCNTs are used as conducting fillers so as to increase the polymer's dielectric constant according to the micro-capacitor model, thereby augmenting both DC electrical conductivity and AC dielectric property of the nanocomposite. The proposed immunosensing platform comprises of PPY/f-MWCNT modified interdigitated microelectrode (IDμEs) array, on which anti-UCHL1-antibodies are immobilized using suitable covalent chemistry. The AC electrical characterization of the nanocomposite modified IDμEs, with and without the antibodies, was performed through generic capacitance vs. frequency (C–F, 1 KHz – 1 MHz) and capacitance vs. applied bias (C–V, 0.1 V–1 V) measurements, using an Agilent B1500A parametric analyzer. The binding event of UCHL1 peptides to anti-UCHL1-antibodies was transduced in terms of normalised changes in parallel capacitance, via the C–F analysis. Further, we have tested the detection efficiency of the said immunoassay against UCHL1 spiked human plasma samples in the concentration range 10 fg/mL – 1 μg/mL. The proposed sensing platform detected UCHL1 in spiked-plasma samples linearly in the range of 10 fg/mL – 1 ng/mL with a sensitivity and LoD of 4.22 ((ΔC/C0)/ng.mL−1)/cm2 and 0.363 fg/mL, respectively. Further, it showed excellent stability (30 weeks), repeatability, reproducibility, selectivity and interference-resistance. The proposed approach is label-free, and if desired, can be used in conjunction with DC measurements, for biosensing applications.

Spin-glass behavior in Li3NiCuBiO6: a two-dimensional distorted honeycomb-lattice

We report a detailed experimental study on the structural and magnetic properties of Li3NiCuBiO6 by means of various characterization techniques. It crystallizes into a monoclinic crystal structure composed of a layered magnetic honeycomb lattice along the c-axis. The existence of glassy state below 4 K is indicated by dc and ac susceptibility measurements. Magnetic contribution to the total heat capacity also peaks around the freezing temperature, and its linear temperature dependence backs our claim of a glassy state in the compound. The calculated magnetic entropy unveils that only ∼26% of the total entropy is released for the system (), and a tremendous amount of spin entropy is still retained in the system. Further, analysis of the frequency-dependent freezing temperature with the help of power law confirms the presence of a spin glass state. Moreover, the appearance of magnetic memory and relaxation effect below freezing temperature manifest the development of the system via a large number of intermediate metastable states. All these measurements confirm the spin-glass behavior of the compound. We consider the presence of different magnetic atoms in honeycomb lattice as the main driving factor for the spin-glass ground state.