Dependence Of Critical Current Density Research Articles

Pulse-width dependent critical current density and the depinning probability of a magnetic skyrmion by spin-polarized currents

Pulse-width dependent critical current density and the depinning probability of a magnetic skyrmion by spin-polarized currents

Comparison of the Field Trapping Ability of MgB2 and Hybrid Disc-Shaped Layouts.

Superconductors have revolutionized magnet technology, surpassing the limitations of traditional coils and permanent magnets. This work experimentally investigates the field-trapping ability of a MgB2 disc at various temperatures and proposes new hybrid (MgB2-soft iron) configurations using a numerical approach based on the vector potential (A→) formulation. The experimental characterization consists in measurements of trapped magnetic flux density carried out using cryogenic Hall probes located at different radial positions over the MgB2 sample, after a field cooling (FC) process and the subsequent removal of the applied field. Measurements were performed also as a function of the distance from the disc surface. The numerical modelling of the superconductor required the evaluation of the critical current density dependence on the magnetic flux density (Jc(B)) obtained through an iterative procedure whose output were successfully validated by the comparison between experimental and computed data. The numerical model, upgraded to also describe the in-field behavior of ARMCO soft iron, was then employed to predict the field-trapping ability of hybrid layouts of different shapes. The most promising results were achieved by assuming a hollow superconducting disc filled with a ferromagnetic (FM) cylinder. With such a geometry, optimizing the radius of the FM cylinder while the external dimensions of the superconducting disc are kept unchanged, an improvement of more than 30% is predicted with respect to the full superconducting disc, assuming a working temperature of 20 K.

Temperature dependence of transport critical current density for REBCO superconducting tapes deposited by MOCVD

The temperature-dependent transport critical current density () behavior of REBa2Cu3O7−δ (REBCO) superconducting tapes with various RE substitutions and combinations has been systematically studied in the temperature range of 4 K–77 K. The measured values were found to be highly in accordance with with the values of the exponent coefficients s ranging from 1.9 to 2.6 in the magnetic-field range of 1–5 T depending on RE ion(s), revealing the dominative pinning mechanism of flux core pinning. The RE-ionic-radius (r) dependences of showed reversed trends for temperatures below and above 50 K, with increasing with r at higher temperatures while it decreased with r at lower temperatures, which was consistent with previously reported results. In particular, the in-field of REBCO tapes at 4 K as a function of r was consistent with the –r trend for low temperatures. We propose to attribute the –r trends to the higher charge carrier density and the lower critical transition temperature () in REBCO films with smaller r. The Gd0.5Yb0.5BCO tape with superior at low temperatures exhibited the furthest diversion from the –r trendlines due to enhanced correlated pinning by the high-density of vertically aligned second-phase nanocolumns in the film. The temperature dependence of for REBCO tapes with a larger r was found to be more susceptible to the magnetic field. Meanwhile, the exponent coefficients s showed a more precipitous increase with the increasing magnetic field, partially due to the lack of effective pinning defects, which was also confirmed by the two-dimensional x-ray diffraction patterns and the higher α values. This work contributes to the study of the of REBCO superconducting tapes below 20 K and leads to a deeper understanding of the temperature-dependent behavior of REBCO films with various RE substitutions and combinations. This provides more comprehensive guidelines for the optimization of RE ions in REBCO for applications at specific temperatures and magnetic fields.

Ic measurement of twisted multifilamentary MgB2 wires with non-magnetic sheath over a wide range of temperatures and fields

All-superconducting rotating machines have the potential for meeting the high power density and high efficiency required for electrical aircraft applications. However, very high AC loss encountered in superconducting armature windings could hinder their development. Multifilamentary MgB2 wires are one of the promising candidates for the stator windings, due to their potentially low AC loss properties with small filament size and twist pitches. As the first step, the dependence of critical current and n-value on magnetic fields and temperatures Ic(B, T) and n(B,T), which are basic input parameters for AC loss simulation, needs to be measured. In this work, we present transport Ic measurements in three non-magnetic multifilamentary MgB2 wires (MgB2/Nb/CuNi/CuZn): one large wire with a 0.70 mm diameter and 25 mm twist pitch, and two small wires with a 0.48 mm diameter each and a 10 mm and 30 mm twist pitch respectively. A four-probe direct current method is used to measure Ic of the MgB2 wires with variations in temperature (15 – 35 K) and magnetic field (0 – 5.5 T). Full Ic data for the small wire with 10 mm twist pitch was obtained, and the n-values were mostly less than 20. While the Ic data for the large wire at low fields was more limited due to heating, the n-values were higher and could be up to around 100. The difference is attributed to the different filament sizes. Experiments also found that there is no significant hysteresis in the transport critical current measured by decreasing or increasing magnetic fields due to the non-magnetic sheaths. This non-hysteretic characteristic is critical for lowering AC loss because the additional losses from magnetic sheaths can be eliminated. From the magnetic-field dependence of critical current density, an empirical expression has been developed that provides suitable extrapolations to lower fields for the large wire.

Large-scale vibrating coil magnetometer for the magnetic characterization of bulk superconductors

This work presents the design and validation of a vibrating coil magnetometer for the characterization of the field dependence of the critical current density of centimeter-sized bulk superconductors as an alternative to the destructive methods typically used. The magnetometer is also shown to be capable of measuring the magnetic moment in an applied field of up to 5 T for diverse magnetic materials, such as soft and hard ferromagnets and high-temperature superconducting pellets. The vibrating coil magnetometer was first optimized using finite element simulations and calibrated using a commercial vibrating sample magnetometer. The vibrating coil magnetometer was benchmarked with hysteresis measurements of a Nd2Fe14B disk made with a commercial hysteresisgraph, showing good agreement between the different setups. The magnetic hysteresis of a YBa2Cu3O7−x superconducting pellet was measured at 77 K, showing a penetration field of 1 T and an irreversibility field of 4 T. The field dependent critical current density of the superconductor was then inferred from the magnetic hysteresis measurements and extrapolated at low fields. Finally, the resulting critical current density was used to successfully reproduce the measured magnetization curve of the pellet at 2 T with finite element simulations.

Superconducting Magnetic Energy Storage for Pulsed Power Magnet Applications

As part of the exploration of energy efficient and versatile power sources for future pulsed field magnets of the National High Magnetic Field Laboratory-Pulsed Field Facility (NHMFL-PFF) at Los Alamos National Laboratory (LANL), the feasibility of superconducting magnetic energy storage (SMES) for pulsed-field magnets and other pulsed power loads is examined. Basic SMES parameters needed to power one of the coil groups of the large 100 T magnet were determined. A circuit topology for the power transfer between the SMES and the magnet was devised, and the basic performance of the topology was simulated to reproduce the pulse shape currently used in the 100 T magnet. The Finite element analysis (FEA) method was used to calculate the magnetic field distribution of several preferred coil configurations for effective SMES design. Magnetic field distribution and the field dependent critical current density of commercial high temperature superconducting (HTS) tapes were used to understand the conductor/cable requirements for the SMES.

Effect of thickness on the superconducting properties of the thin films of FeTe0.55Se0.45 deposited on YSZ substrates using Pulsed laser deposition (PLD) technique

We report the successful fabrication of thin films of thickness ∼26 nm, 59 nm, 76 nm, and 158 nm of the composition FeTe0.55Se0.45 on the (100)-oriented Yttria-stabilized zirconia (YSZ) substrate using the pulsed laser deposition (PLD) technique. The effect of thickness on the structure and superconducting properties of the thin films has been investigated. X-ray diffraction study reveals the growth of thin films along the c-axis. The temperature-dependent resistivity measurements confirm superconductivity in all the fabricated thin films, and the highest ∼ 16.2 K has been observed for the thin film of thickness ∼59 nm, which is higher than the corresponding value of the polycrystalline target sample. The superconducting parameters such as upper critical magnetic field coherence length thermally activated energy (TAE) U0, and vortex phase state have been measured by magnetotransport measurements near in the different applied magnetic fields up to 12 T. The TAE values determined from the conventional and modified thermally activated flux flow (TAFF) models are discussed and compared. A crossover from 2-dimensional (2D) vortex to 3-dimensional (3D) vortex behaviour has been observed. The vortex phase diagrams are used to observe the transition from the vortex liquid to the vortex glass state in the grown thin films. Moreover, magnetoresistance (MR) measurements show non-saturating linear magnetoresistance (LMR) in the high field region, indicating the presence of the possible topological state in the grown thin films. The values of magnetic field dependent transport critical current density, have been evaluated from the current-voltage (I-V) curves. Furthermore, the normalised pinning force density has been used to characterize the pinning processes using the Dew Hughes’ scaling rule which reveals that the grown thin films contain δl-surface pinning centers.

Thermomagnetic instabilities in 3D network of superconducting lead nanofilaments in porous glass

Thermomagnetic instabilities in the lead-porous glass (Pb-PG) nanocomposite in superconducting state were studied, and a model was proposed that relates magnetization jumps and heat release spikes with average critical current density. The samples were created by filling porous glass (characteristic pore size d = 7 nm) with lead from a melt under pressure, which created a 3D multiply connected system of lead filaments. The critical temperature of superconducting transition in Pb-PG T c = 7.2 K is the same as for bulk lead and the critical magnetic field H c (0) ≈ 40 kOe is much higher than H c bulk (0) ≈ 800 Oe for bulk lead. Hysteresis and magnetic flux jumps were observed in the magnetization curves m(H) of the Pb-PG nanocomposite, which are connected with the formation of magnetic flux gradients in a system of interconnected contours. Magnetic flux jumps are thermomagnetic processes accompanied by heat release which was directly observed by measuring adiabatic temperature change in the sample during magnetic field sweep. The flux jumps in the magnetization and heat release events were almost periodic in the magnetic field. The period dependences on the magnetic field are similar to the calculated average critical current density dependence j c (H).

Fabrication and characterization of NbN/(TaN/NbN) N stacked Josephson junctions

In this work, we present a detailed study of the electrical properties of stacked NbN/(TaN/NbN) N Josephson junctions. Cross-sectional scanning transmission electron microscopy analysis of the 5-stacked junction shows that the multilayer interface is very flat, each barrier has the same thickness, and the sidewalls of the junctions are nearly perpendicular to the substrate. Stacked junctions of different sizes and stacking numbers all have only one transition in their current–voltage curves. This indicates that the critical currents of the junctions in the stacked junctions are almost the same, showing the stability and repeatability of the multilayer fabrication and etching process. At 4.2 K, the 4-stacked junction shows excellent Josephson properties with characteristic voltage V c of 3.54 mV, which is about four times the 0.88 mV of the single junction. The temperature dependence of critical current density J c and V c of the stacked junction with N = 1, 2, 4 were measured, all of which can be fitted with dirty-limit theory. Stacked junctions with larger V c or more stacked layers can be achieved by optimizing electrode and barrier thickness, barrier resistivity, and thermal relaxation rate, etc.

On the Temperature- and Magnetic Field–Dependent Critical Current Density of Compressed Hydrogen Sulphide

On the Temperature- and Magnetic Field–Dependent Critical Current Density of Compressed Hydrogen Sulphide

The superconducting properties of YBa2Cu3Oy ceramics fabricated using ultrahigh dilution technology

YBa2Cu3Oy (Y-123) is one of the most intensively studied high-temperature superconductors (HTS) and has great potential for applications in electronics. Its superconducting properties significantly depend on the oxygen index (y), the peculiarities of the atomic crystal and microgranular structure, the type and concentration of contaminating atoms. Therefore, of particular interest are the techniques of HTS synthesis that significantly affect the superconducting properties, as well as modifications of these techniques. The aim of this study was to investigate the effect of ultrahigh dilution (UHD) technology on the Y-123 HTS properties.We applied UHD technology to treat Y2O3·4BaO2·6CuO composition (before and/or after calcination) and used solid-phase reaction to obtain batches of ceramic samples of the Y-123 phase. Main characteristics of the synthesized HTS specimens (the orthorhombic unit cell parameters, temperature dependence of electrical resistance, Meissner effect, and critical current density) were studied.X-ray phase analysis demonstrated that the samples were practically single-phase and consisted of the Y-123 phase. Depending on the treatment method, the modifying effect varied. Positive and most significant results were demonstrated for specimens obtained from precursor powder mixture treated with UHD. For some of such specimens an increase in the temperature of the beginning of the transition to the superconducting state by 3.8 K, the Meissner effect by 9%, and the density of the intergranular critical current by 35% were observed. We conclude that UHD technology can be used to improve properties of HTS. However, methodology for implementation of UHD technology should depend on which specific superconductor property needs to be changed.

Investigation of high-energy ultrasonication of RE 2BaCuO5 (RE = Y, Gd) on the growth and superconducting properties of REBa2Cu3O7−δ top-seeded melt textured bulks

Recently, an improvement in the flux pinning performance of REBa2Cu3O7−δ (REBCO) bulk was achieved employing high energy ultrasonic irradiation (up to 300 W and 60 min) prior to the infiltration-growth process. Here, we demonstrate that a higher ultrasonic power and shorter duration treatment (450 W for 30 min) of the RE 2BaCuO5 (RE211, RE= Y, Gd) powder produces individual, nanometer-sized and surface damaged RE211 particles (RE211Ultra). We study the growth of YBCO and GdBCO systems via the top-seeded melt-growth method, with the addition of 30 mol% of RE211Ultra, which were pre-treated by high-energy ultrasonication and compared with the conventional method. Isothermal growth experiments clarified that the addition of RE211Ultra particles enables faster and more effective crystal growth via an improved peritectic reaction due to their size in the nanometer range and presence of sharp edges, which are crucial for growing large, single grain bulks of REBCO. Microstructural investigations by scanning electron microscopy indicated the presence of two differently sized RE211 inclusions within the bulk GdBCO and YBCO superconductors. All samples showed an onset of superconductivity at ∼92 K or above. Utilizing the effective growth temperature window and the addition of RE211Ultra, single grain bulks of GdBCO and YBCO were fabricated by the slow-cooling method. The field dependent critical current density (J c) of the bulk samples using RE211Ultra were found to exhibit superior performance over the standard GdBCO/YBCO samples due to significant changes of sample growth and of their microstructures. Here, we discuss various factors affecting the addition of RE211Ultra on the development of the microstructure, growth of bulk, single grain materials and further, the superconducting properties of different REBCO superconductors.

Temperature dependence of the self-field critical current densities and flux pinning in YBa2Cu3O7–δ thin films containing nanoprecipitates

The temperature dependence of the self-field and in-field critical current densities Jc(T) was investigated in YBa2Cu3O7–δ thin films containing a high density of nanoprecipitates. The self-field Jc(T) and in-field Jc(T) were both approximated by Jc(T) ∼ (1 – T/Tc)m (1 + T/Tc)2, where the index m was mostly 2.0–2.6 in moderate magnetic fields (µ0H = 0.5–1 T, // c-axis), but m was smaller (1.5–1.8) in self-fields. This phenomenon can be explained by the assumption that the self-field Jc is determined by the flux pinning by relatively large nanoprecipitates, which is supported by simple theoretical calculations of the elementary pinning force fp due to the core pinning interaction. The self-field Jc is estimated to be proportional to 1/λ3, where λ is the penetration depth. This relationship can successfully explain the previously observed inverse correlation between the self-field Jc and the surface resistance Rs that is supposed to be proportional to λ3.

Effects of TiO2 nanoparticle addition on the flux pinning properties of the Bi1.6Pb0.4Sr2Ca2Cu3O10+δ ceramics

The effects of adding TiO2 nanoparticles on the flux pinning properties of the Bi–Pb–Sr–Ca–Cu–O (BPSCCO) system were investigated. Polycrystalline samples of (Bi1.6Pb0.4Sr2Ca2Cu3O10+δ)1-x(TiO2)x, where x = 0.000, 0.002, 0.004, 0.006, 0.008, and 0.010, were fabricated by the conventional solid-state reaction method. The X-ray diffraction (XRD) results showed that all samples consisted of Bi-2223 and Bi-2212 phases. The Bi-2223 volume fraction decreased with the addition of TiO2. Scanning electron microscopy (SEM) examination presented a degradation in texture structure with increasing misoriented grain and porosity with high doping contents. The critical temperature was decreased by TiO2 appearance in relation to Bi-2223 deceleration. Critical current density dependence on the magnetic field Jc(B) was enhanced with x = 0.002, 0.004 and reached maximal values on the x = 0.002 sample. In the collective pinning theory framework, the small bundle field (Bsb) and the large bundle field (Blb) were estimated, revealing the extension of the small and large bundle regimes with proper amounts of dopant. The temperature-dependent normalized critical current density (j) indicated that δl pinning is the dominant flux pinning mechanism in all samples. The Dew-Hughes model analyzed the pinning center properties and confirmed that TiO2 nanoparticles create normal core point pinning centers in the matrix.

Design and modelling tools for DC HTS cables for the future railway network in France

The use of high-temperature superconducting (HTS) cables in power systems increases the transmission capacity, whereas reducing the volume of the installation. In addition, in high current applications, HTS cables considerably reduce power losses, right-of-ways and total system mass. This paper presents different multi-physics studies to be performed to accurately design the direct current (DC) HTS cables for the future railway network planned by the French company SNCF. The process used to design DC cables for high operating current (between 5 kA and 20 kA at 1750 V) made of commercial (RE)BaCuO tapes is presented. In this design process, the critical current density dependence J c(B, θ, T) of the superconducting tapes, the thermal properties of the materials used as well as different cable cooling configurations are considered. Finally, we discuss the selection of the appropriate cooling configuration to ensure adequate cooling of the cable.

Thickness dependence of structural and superconducting properties of Co-doped BaFe2As2 coated conductors

SummaryHigh-quality Co-doped BaFe2As2 thin films with thickness up to 2 μm were realized on flexible metal tapes with LaMnO3 as buffer layers fabricated by an ion beam-assisted deposition technique. Structural analysis indicates that increasing thickness does not compromise the film crystallinity, except for a small amount of impurities. Two types of thickness dependence of critical current density (Jc) were found: one is almost thickness independent in the range of 0.6–1.5 μm and the other is highly thickness dependent. In addition, the maximum value for crucial current Ic at 9 T and 4.2 K is about 55 A/12 mm-W for the 1.5-μm-thick film. Anisotropic Ginzburg–Landau scaling demonstrates that dominant pinning centers develop from correlated to uncorrelated with increasing film thickness. The further theoretical analysis shows that with film thickness increasing the pinning mechanism evolves progressively from a δl pinning to the δTc pinning mechanism.

Anisotropic Critical Current Densities in Ba0.6K0.4Fe2As2 with Splayed Columnar Defects

Enhancement and non-monotonic field dependence of critical current density (Jc ), called anomalous peak effect, were observed in Ba1−x K x Fe2As2 with splayed columnar defects. In principle, anisotropy of in-plane Jc should be present in this superconductor since the introduced splayed columnar defects introduce anisotropy in the plane. This study reports in-plane anisotropy of Jc observed in 2.6 GeV U irradiated Ba0.6K0.4Fe2As2 with splay angles of ±15° and ±20°. Results show that Jc component parallel to the splay plane is larger than the perpendicular component, and the parallel component contribute to the anomalous peak effect at around B Φ/3 more.

Peak Effects in 2H-NbSe2 Single Crystals Induced by Particle Irradiations

Effects of three kinds of columnar defects in NbSe2 single crystals introduced by 320 MeV Au irradiation with a dose equivalent matching field B Φ up to 4 T were studied. Through the magnetization measurement using a SQUID magnetometer, two pronounced peak effects in the external field dependence of critical current density (J c) were observed in crystals introduced with splayed and tilted columnar defects. In crystals with splayed columnar defects, J c at the peak field reaches the maximum for splay angle θ CD = ±10°, which is a little different from that found in YBa2Cu3O7 and iron-based superconductors, where optimal θ CD is equal to ±5°.

A New Microscopic Approach To Deal with the Temperature- and Applied Magnetic Field–Dependent Critical Current Densities of Superconductors

Based on the formalism of the Bethe-Salpeter equation, we present here a new approach to deal with the temperature (T)- and the applied magnetic field (H)-dependent critical current densities (jcs) of superconductors (SCs). Saliently, it employs (i) the premise that the chemical potential μ (T, H) subsumes most of the factors to which the widely varying empirical values of jc (T, H) of an SC are conventionally attributed, (ii) the basic equation that defines jc as a product of the electronic charge, the number density of superconducting electrons (ns) and their critical velocity (vc), (iii) a recently derived equation for ns (T, H), and (iv) the empirical values of jc (T, H)—which it is meant to explain—as inputs into one of its equations which, paradoxical though it may seem, is shown to have the virtue of shedding light on several parameters related to jc (T, H), such as μ, ns, vc, m*, nL, and λm, where m* is the effective mass of an electron, nL the number of occupied Landau levels, and λm the magnetic interaction parameter. Remarkably, the approach is found to lead to two branches of μ-dependent solutions with distinctly different values of the parameters corresponding to the same value of jc (T, H). This is reminiscent of the behavior of the chemical potential in SCs with a low density of charge carriers that was reported by Marel [Physica C 165, 35 (1990)] and described as anomalous. Finally, we show that our approach suggests the exciting possibility of fabricating an SC that has a bespoke value of jc at suitably chosen values of T and H. For the sake of concreteness, we employ here some of the available empirical data on the jc (T, H) values of Bi-2212.

Estimation of the Electricity Storage Volume Density of Compact SMESs of a New Concept Based on Si Microfabrication Technologies

A compact superconducting magnetic energy storage system (SMES) produced by Si micro fabrication technologies has been proposed to improve electricity storage volume density, w, in the sub-Wh/L range of conventional SMESs and to produce them at a low cost by mass production. In parallel with the experimental development reported previously, a series of trials was performed to estimate a feasible value of w based on the calculation of the magnetic field generated by the compact SMES by improving the calculation models step by step. In this work, the experimentally obtained magnetic flux density dependence of superconductive critical current density was taken into consideration for the first time in this series of trials, together with the additional improvement of the calculation models. The results of the estimation indicated that a compact SMES produced by the proposed concept can attain a w in the Wh/L range or more, ranking with or surpassing that of presently used capacitors.