Jc Behavior Research Articles

Cultivating Well-being of Nurses Through Job Crafting: The Moderating Effect of Job and Personal Resources

We look into the way nurses’ job crafting perception (POC) affects their job crafting behaviour (JC) and, as a result, their well-being (WB). Further, the moderating function of personal and job resources (JR) is also scrutinised. We collected primary data from 773 nurses working in 12 private sector and public sector hospitals in Northern Indian states using a standardised questionnaire and deployed structural equation modelling to examine the hypothesised linkages. The empirical findings exposed that POC significantly predicts JC. Second, JC significantly ameliorates nurses’ hedonic and eudaimonic WB. Finally, personal resources (PR) intensify the influence of POC on JC, whereas JR do not. The findings imply that POC cultivates nurses’ JC behaviour, which, in turn, enhances their WB and PR catalyses this driver impact.

Enhanced critical current density and flux pinning of anthracene doped magnesium diboride superconductor

The present investigation reports the structural, superconducting and flux pinning properties of anthracene doped MgB2 superconductor prepared by powder-in-sealed-tube (PIST) method. The formation of the hexagonal structure of MgB2 is confirmed from the XRD analysis of all the synthesized samples. The microstructural changes by anthracene doping in the MgB2 superconductor are studied using FESEM, TEM and Raman analysis. Raman spectra show the change in the E2g peak frequency in all the doped samples. All the samples show a sharp superconducting transition and the critical temperature (Tc) of anthracene doped samples decreases. The Jc(B) behavior at 10 and 20 K shows a significant enhancement in the anthracene doped samples as compared to undoped MgB2. 3 wt% anthracene doped MgB2 shows maximum enhancement in Jc at 10 and 20 K, i.e., 7.03 × 105 and 2.5 × 105A∕cm2 at 2 T, while 5 wt% anthracene doped sample (MBA5) shows lower Jc(B) characteristics. The grain boundary pinning is the dominant pinning mechanism in all the synthesized samples.

Influence of variable Ca-doping on the critical current density of low-angle grain boundaries in YBa2Cu3O7−d

The rapid decrease in the critical current density Jc with grain boundary (GB) misorientation angle θ strongly limits the current-carrying capability of yttrium–barium–copper-oxide (YBCO), and the residual low-angle GB distribution is the most important current-limiting mechanism in biaxially textured YBCO coated conductors. To deepen the understanding of the Ca doping in low-angle GBs in YBCO, transport characteristics of low-angle GBs in YBa2Cu3O7−d bicrystals with different Ca contents x (Y1−xCaxBa2Cu3O7−d) were examined to verify the influence of the carrier density at the GB due to the Ca doping level. Y1−xCaxBa2Cu3O7−d (x = 0, 0.10, 0.15, and 0.30) epitaxial films were deposited by pulsed laser deposition on single crystal SrTiO3 (STO) substrates and 7° and 9° symmetric [001]-tilt bicrystal STO substrates. We found that 15% Ca doping was the most effective at increasing the Jc behavior across the 7° GB in intermediate fields, completely eliminating the GB dissipation signature in the V–I characteristics. For the 9° GB, 10% Ca doping yielded the highest depairing current Jd across the GB, calculated from the flux flow resistivity, even though a significant GB dissipation signature remained in the V–I curves.

YBa2Cu3O7−x films with Ba2Y(Nb,Ta)O6 nanoinclusions for high-field applications

The structural and transport properties of YBa2Cu3O7−x films grown by pulsed laser deposition with mixed 2.5 mol% Ba2YTaO6 (BYTO) and 2.5 mol% Ba2YNbO6 (BYNO) double-perovskite secondary phases are investigated in an extended film growth rate, R = 0.02–1.8 nm s−1. The effect of R on the film microstructure analyzed by TEM techniques shows an evolution from sparse and straight to denser, thinner and splayed continuous columns, with mixed BYNO + BYTO (BYNTO) composition, as R increases from 0.02 nm s−1 to 1.2 nm s−1. This microstructure results in very efficient flux pinning at 77 K, leading to a remarkable improvement in the critical current density (Jc) behaviour, with the maximum pinning force density Fp(Max) = 13.5 GN m−3 and the irreversibility field in excess of 11 T. In this range, the magnetic field values at which the Fp is maximized varies from 1 T to 5 T, being related to the BYNTO columnar density. The film deposited when R = 0.3 nm s−1 exhibits the best performances over the whole temperature and magnetic field ranges, achieving Fp(Max) = 900 GN m−3 at 10 K and 12 T. At higher rates, R > 1.2 nm s−1, BYNTO columns show a meandering nature and are prone to form short nanorods. In addition, in the YBCO film matrix a more disordered structure with a high density of short stacking faults is observed. From the analysis of the Fp(H, T) curves it emerges that in films deposited at the high R limit, the vortex pinning is no longer dominated by BYNTO columnar defects, but by a new mechanism showing the typical temperature scaling law. Even though this microstructure produces a limited improvement at 77 K, it exhibits a strong Jc improvement at lower temperature with Fp = 700 GN m−3 at 10 K, 12 T and 900 GN m−3 at 4.2 K, 18 T.

Polymer-assisted surface decoration for critical current enhancement in YBa2Cu3O7−x films

In this study, chemically decorated surfaces are employed as tools for Artificial Pinning Centres (APC) introduction in superconducting YBa2Cu3O7−x (YBCO) films. Self-assembled oxide nanostructures are grown on crystalline substrates via a very versatile and low-cost chemical technique called Polymer Assisted Deposition (PAD). Such decorated templates are used, in a second step, as substrates for YBCO film growth via Metal Organic Decomposition (MOD) or Pulsed Laser Deposition (PLD). The aim of the structures is to produce in the superconducting matrix strain and/or defects that should act as APCs and therefore enhance the transport properties of the samples. The oxides selected for the decoration are commonly used for the introduction of artificial pinning centres in YBCO: BaZrO3 and ZrO2. The decorated surfaces are analyzed via Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM). YBCO films have been characterized via SEM, X-Ray Diffraction (XRD), Transmission Electron Microscopy (TEM), DC resistivity and critical current measurements. The results show that the nanostructures are stable and that they can efficiently introduce strain and stacking faults in the film. This causes an increase in the value of the critical current density Jc and better in-field behaviour in all the investigated field range, compared to the analogous film grown on a standard substrate, especially for chemically derived YBCO. Also Jc angular dependence measurements, Jc(θ), show an isotropic enhancement of the critical current for every angle of application of the field.

Large and significantly anisotropic critical current density induced by planar defects in CaKFe4As4 single crystals

Three independent components of critical current density, one for the H//c axis and the other two for the H//ab plane, have been studied in CaKFe4As4 single crystals. When the magnetic field is applied along the c axis, we observed fish-tail-like peaks in the M-H hysteresis loop, and the magnetization at higher temperatures exceeds that at lower temperatures at high fields. When the field is applied parallel to the ab plane, a dip structure is observed in the M-H hysteresis loop near the self-field. In addition, for the H//ab plane, we succeeded in separately evaluating the large and significantly anisotropic in-plane and out-of-plane Jc. Transmission electron microscopy revealed the presence of planar defects parallel to the ab plane in CaKFe4As4, which have not been observed in any other iron-based superconductors. We discuss the possible relationship between the anomalous Jc behavior and the planar defects.

Anomalies in vortex lattice dynamics driven by induced ac currents in superconducting films with magnetic arrays of two-fold symmetry

We study the dynamics of the vortex lattice driven by ac induced currents in the critical state regime, for T > 0.70 TC. The samples are superconducting films grown on top of two-fold symmetry array of magnetic dots. In these heterostructures, the induced ac currents flow parallel to the short and to the long side of the pinning array in different areas of the samples simultaneously. This behavior produces remarkable effects in the vortex lattice dynamics. First of all, periodic features are observed in the ac susceptibility versus applied magnetic field measurements which are related to matching effects between the vortex lattices and the magnetic array. However, the vortex lattice reconfiguration observed in magnetotransport experiments is absent. Some of these features are revealed as maxima instead of being minima, indicating higher mobility at certain matching fields. Competing unstable vortex configurations could lead to increase vortex mobility precluding the reconfiguration transition. At high temperatures, where the matching effects show up, the magnetic permeability of the dots is the mechanism that governs the JC(T) behavior. Moreover, the temperature dependence of the pinning force FP(T) shows a temperature crossover related to an unexpected enhancement in vortex mobility. Vortex–vortex interaction and the interplay between trapped and interstitial vortices are a hint to explain these phenomena.

Co-addition of nano-carbon and nano-silica: An effective method for improving the in-field properties of magnesium diboride superconductor

MgB2 superconductor sample co-doped with nano-carbon (n-C) and nano-silica (n-SiO2) is prepared and its structural and superconducting properties are compared with pure and n-C and nano SiC (n-SiC) mono-doped samples. Shrinkage of a-lattice parameter is observed for all doped samples, among which the co-doped sample exhibits the maximum shrinkage, an evidence of effective carbon substitution at boron sites. All doped samples show significantly enhanced in-field critical current density JC(H), where the co-doped sample dominates others throughout the whole range of field studied. Lattice strains induced by carbon substitution and flux pinning caused by uniformly distributed nano sized Mg2Si particles formed by the reaction between Mg and n-SiO2, are the main reasons for the highly enhanced JC(H) behavior of the co-doped superconductor.

Study of superconducting properties of ferrocene‐added MgB2

In the present study, we have shown the effects of ferrocene (FeC10H10) addition on the superconducting properties of polycrystalline MgB2 superconductor using transport and magnetic measurements. The addition of FeC10H10 up to 2 wt% in the MgB2 sample has shown enhanced critical current density, JC in the entire magnetic field region without affecting much the transition temperature. At 10 K, with respect to a pristine MgB2 sample, JC has improved by a factor of 6.55 at 6 T applied field for 1 wt% FeC10H10. An improvement in the upper critical field, and irreversibility field, Hirr has also been observed up to 2 wt% addition of FeC10H10. The value of as obtained using the Ginzburg–Landau (GL)‐theory fit of the experimental data increases by almost 2 T for 2 wt% FeC10H10‐added MgB2 as compared to the pristine samples. From X‐ray photoemission spectroscopy (XPS), we observed that the Fe is present in sample in the form of ferromagnetic oxides, Fe3O4 and γ‐Fe2O3. These ferromagnetic inclusions provide efficient pinning centers to improve JC(H) behavior. The flux pinning mechanisms present in the FeC10H10‐added samples are described and discussed in this paper.

MgB2 coated conductors directly grown on flexible metallic Hastelloy tapes by hybrid physical–chemical vapor deposition

MgB2 coated conductors (CCs), which can avoid the low packing density problem of powder-in-tube (PIT) processed wires, can be a realistic solution for practical engineering applications. Here we report on the superior superconducting properties of MgB2 CCs grown directly on the flexible metallic Hastelloy tapes without any buffer layer at various deposition temperatures from 520 to 600 °C by using hybrid physical–chemical vapor deposition (HPCVD) technique. The superconducting transition temperatures (Tc) are in the range of 38.5–39.4 K, comparable to bulk samples and high quality thin films. Clear (101) and (002) reflection peaks of MgB2 are observed in the X-ray diffraction patterns without any indication of chemical reaction between MgB2 and Hastelloy tapes. From scanning electron microscopy, it was found that connection between MgB2 grains and voids strongly depend on the growth temperature. A systematic increase in the flux pinning force density and thereby the critical current density with decreasing growth temperature was observed for the MgB2 CCs. The critical current density (Jc) of Jc(5 K, 0 T) ∼107 A/cm2 and Jc(5 K, 2.5 T) ∼105 A/cm2 has been obtained for the sample fabricated at a low growth temperature of 520 °C. The enhanced Jc (H) behavior can be understood on the basis of the variation in the microstructure of MgB2 CCs with growth temperature.

Critical current density: Measurements vs. reality

Different experimental techniques are employed to evaluate the critical current density (Jc), namely transport current measurements and two different magnetisation measurements forming quasi-equilibrium and dynamic critical states. Our technique-dependent results for superconducting YBa2Cu3O7 (YBCO) film and MgB2 bulk samples show an extremely high sensitivity of Jc and associated interpretations, such as irreversibility fields and Kramer plots, which lose meaning without a universal approach. We propose such approach for YBCO films based on their unique pinning features. This approach allows us to accurately recalculate the magnetic-field–dependent Jc obtained by any technique into the Jc behaviour, which would have been measured by any other method without performing the corresponding experiments. We also discovered low-frequency–dependent phenomena, governing flux dynamics, but contradicting the considered ones in the literature. The understanding of these phenomena, relevant to applications with moving superconductors, can clarify their dramatic impact on the electric-field criterion through flux diffusivity and corresponding measurements.

Jc improvement by double artificial pinning centers of BaSnO3 nanorods and Y2O3 nanoparticles in YBa2Cu3O7 coated conductors

Double artificial pinning centers of BaSnO3 nanorods and Y2O3 nanoparticles were investigated in YBa2Cu3O7 films on textured substrates prepared using ion beam assisted deposition. The BaSnO3 and Y2O3 content was varied in pulsed laser deposition. Transmission electron microscopy observation revealed the systematic change in density of the BaSnO3 nanorods and the Y2O3 nanoparticles in the films. In YBa2Cu3O7 + BaSnO3 films, maximum global pinning force (Fp,max) was improved at high magnetic fields, and Fp,max was shifted to high magnetic field by the Y2O3 incorporation due to an increase in density of the pinning centers. The angular dependences of critical current density (Jc) in the YBCO + BaSnO3 films were tuned by introducing Y2O3, and some of the YBa2Cu3O7 + BaSnO3 + Y2O3 films exhibited isotropic Jc behavior at low magnetic field. The double artificial pinning centers of BaSnO3 nanorods and Y2O3 nanoparticles are effective in improving Jc angular dependences, Jc values at high magnetic fields, and Fp,max.

Effect of SiC‐Impurity Layer and Growth Temperature on MgB2 Superconducting Tapes Fabricated by HPCVD

AbstractThe influence of SiC‐impurity layer and growth temperature on microstructure and superconducting properties are studied for MgB2 superconducting tapes. A pulsed laser deposition (PLD) system is used for the deposition of amorphous SiC‐impurity layers on flexible metallic Cu(001) tapes. The MgB2 superconducting tapes are fabricated by growing MgB2 films on the top of SiC/Cu tapes, over a wide temperature range of 460–600 °C, by using hybrid physical (HP) CVD system. Among all tapes, the MgB2/SiC/Cu tape deposited at a temperature of 540 °C has the highest Tc of ∼37.7 K. Scanning electron microscopy (SEM) images reveal hexagonal‐shaped MgB2 grains with good connectivity, and their sizes are found to vary with growth temperature. When compared to MgB2/Cu tapes, the MgB2/SiC/Cu tapes exhibit an opposite trend in the dependence of critical current density (Jc) with deposition temperatures. The improved Jc(H) behavior can be explained on the basis of the enhanced flux pinning force density (Fp) for MgB2/SiC/Cu tapes upon increasing the growth temperature

Comparison on Effects of ${\rm B}_{4}{\rm C}$, ${\rm Al}_{2}{\rm O}_{3}$, and SiC Doping on Performance of ${\rm MgB}_{2}$ Conductors

Several MgB2 monofilamentary samples are prepared to evaluate the effects that the doping compounds B4C, Al2O3, and SiC have on critical current density (Jc) and the Jc dependency of magnetic flux density (B) of the sample. All of the samples in this study have Nb sheaths and are manufactured using in situ precursor powders and the Powder-in-Tube fabrication method. The amounts of added impurities are 10 wt.% for B4C and Al2O3, and 3, 10, and 20 wt.% for SiC. A reference sample without any doping is also prepared. All of the samples are heat treated between 650 and 800°C for 30 minutes. The transport Jc(B) characteristics are measured at 4.2 K and the magnetic Jc(B) behavior is obtained in varied temperatures up to 30 K. The changes in connectivity, or effective cross-section, are also evaluated by performing resistivity measurements on the samples after removal of the sheath. Furthermore, the pinning forces of the samples are evaluated from the magnetic measurements.

$J_{\rm c}$ Scaling and Anisotropies in Co-Doped Ba-122 Thin Films

We have successfully grown epitaxial, superconducting films of Ba(Fe1-xCox)2As2 (Ba-122)with x ~ 0.1. The films grow without observable correlated defects parallel to the c-axis, as confirmed by TEM. This is also reflected in the absence of a caxis peak in Jc({\theta}). In contrast to cuprate high-Tc superconductors such as YBa2Cu3O7-d or even Bi2Sr2Ca2Cu3O10-d, the pnictides show a rather low anisotropic behavior in their Jc({\theta}) behavior as well as in their upper critical fields, Hc2. As a multiband superconductor, Ba-122 exhibits a temperature dependent electronic mass anisotropy.

Effect of sorbic acid doping on flux pinning in bulk MgB2 with the percolation model

In this paper, we study the doping effect of sorbic acid (C6H8O2), from 0 to 20wt.% of the total MgB2, on critical temperature (Tc), critical current density (Jc), irreversibility field (Hirr) and crystalline structure. The XRD patterns of samples show a slightly decrease in a-axis lattice parameter for doped samples, due to the partial substitution of carbon at boron site. On the other hand, we investigate the influence of doping on the behavior of flux pinning and Jc(B) in the framework of percolation theory and it is found that the Jc(B) behavior could be well fitted in high field region. The two key parameters, anisotropy and percolation threshold, play very important roles. It is believed that the enhancement of Jc is due to the reduction of anisotropy in high field region.

Investigation of lauric acid dopant as a novel carbon source in MgB2 wire

We fabricated lauric acid (LA) doped MgB2 wires and investigated the effects of the LA doping. For the fabrication of the LA-doped MgB2 wires, B powder was mixed with LA at 0–5wt.% of the total amount of MgB2 using an organic solvent, dried, and then the LA-treated B and Mg powders were mixed stoichiometrically. The powder mixture was loaded into an Fe tube and the assemblage was drawn and sintered at 900°C for 3h under an argon atmosphere.We observed that the LA doping induced the substitution of C for the B sites in MgB2 and that the actual content of C increased monotonically with increasing LA doping level. The LA-doped MgB2 wires exhibited a lower critical temperature (Tc), but better critical current density (Jc) behavior in a high magnetic field: the 5wt.% LA-doped sample had a Jc value of 5.32×103A/cm2, which was 2.17 times higher than that of the pristine sample (2.45×103A/cm2) at 5K and 6T, suggesting that LA is an effective C dopant in MgB2 for enhancing the high-field Jc performance.

Inter-granular current in iron-oxypnictide superconductors

Inter- and intragranular currents, Jcinter and Jcintra, in LaFePO0.94F0.06 polycrystalline sample are evaluated by measuring the remanent-state field profile using magneto-optical imaging method. Obtained images show the absence of magnetic field modulation associated with the weak-link nature of grain boundaries, indicating that Jcinter and Jcintra are comparable in magnitude in contrast to other iron-arsenide superconductors. Jcinter is estimated to be 2×104A/cm2 in the limit of T=0K, which is larger than the values in other iron-arsenide superconductors. Implication of these Jc behavior is discussed in relation with possible pairing symmetries.

Magneto-optical imaging of polycrystalline LaFePO1−xFx

The remanent state field profile has been observed in polycrystalline LaFePO0.94F0.06 by magneto-optical (MO) imaging method. MO images show the absence of magnetic field modulation associated with weak-link nature of grain boundaries, indicating that the inter-grain critical current density Jcinter is comparable to intra-grain critical current density Jcintra in contrast to iron-arsenide superconductors. Jcinter is estimated as 1.9×104A/cm2 at T=0K from magnetization measurement, which is similar to the values in iron-arsenide superconductors. Implication of these Jc behavior is discussed in relation to the possible pairing symmetry.

A pinning model and universal pinning regimes in [formula omitted] superconducting films

A model for vortex pinning at boundaries with modulated pinning potentials is developed for high-quality YBa2Cu3O7 superconducting films and multilayers. This model accurately describes the experimentally obtained Jc(Ba) behavior in different films over the entire field and temperature (T) ranges. Deviations are observed at high fields and temperatures due to the thermally activated depinning which is not accounted for by the model. A supplementary “model-free” analysis of the temperature dependent Jc curves leads to the four regions in the field-temperature phase diagram which are attributable to the well-known pinning regimes of collective pinning theory. The results obtained indicate the universality of the pinning model developed, which incorporates the universal pinning regimes and the ability to describe Jc(Ba,T) dependences.