Showing papers on "Flux pinning published in 2023"
TL;DR: In this article , normal-incidence irradiation by 100 MeV Ag ions is used to improve flux pinning in previously optimised commercial REBCO tapes from the American Superconductor Corporation.
Abstract: Normal-incidence irradiation by 100 MeV Ag ions is used to improve flux pinning in previously optimised commercial REBCO tapes from the American Superconductor Corporation. We observe distinct critical-current anisotropy enhancements below and above 40 K. Above 40 K a strong c-axis peak appears in the angular dependence of the critical current, as is usually expected upon the introduction of columnar defects. The critical current is enhanced significantly but only for a limited range of field angles. Close to the parallel-field direction there is no enhancement or even a reduction in critical current. Below 40 K, on the other hand, the enhancement is much broader with respect to field angle, creating an almost isotropic response at 20 K, 3 T. The absence of a prominent c-axis peak does not indicate a lack of pinning, since the absolute value of the critical current still increases by a factor of 2.8 compared to an unirradiated sample. Instead, we postulate that pre-existing point-like pinning centres act to mediate an interaction between the existing planar and newly-introduced columnar pins, broadening both contributions. The point-like pins become less effective with increasing temperature as the coherence length increases, leading to a reduction in this interaction and a separation of the individual peaks relating to planar and columnar pins. At 20 K, we achieve an enhancement in the angular-minimum critical current by a factor of 2.7, in a material that had already been process-optimised for low-temperature pinning.
2 citations
TL;DR: In this article , a non-conventional protocol for the magnetic measurements of superconductors in a SQUID magnetometer and probe the trapped magnetic flux in two near-room-temperature supercondors H 3 S and LaH 10 at high pressures is implemented.
Abstract: Abstract Recent discoveries of superconductivity in various hydrides at high pressures have shown that a critical temperature of superconductivity can reach near-room-temperature values. However, experimental studies are limited by high-pressure conditions, and electrical transport measurements have been the primary technique for detecting superconductivity in hydrides. Here we implement a non-conventional protocol for the magnetic measurements of superconductors in a SQUID magnetometer and probe the trapped magnetic flux in two near-room-temperature superconductors H 3 S and LaH 10 at high pressures. Contrary to traditional magnetic susceptibility measurements, the magnetic response from the trapped flux is almost unaffected by the background signal of the diamond anvil cell due to the absence of external magnetic fields. The behaviour of the trapped flux generated under zero-field-cooled and field-cooled conditions proves the existence of superconductivity in these materials. We reveal that the absence of a pronounced Meissner effect is associated with the very strong pinning of vortices inside the samples. This approach can also be a tool for studying multiphase samples or samples that have a low superconducting fraction at ambient pressure.
2 citations
1 citations
TL;DR: In this paper , the effect of the point pinning effect on low-field magnetization in Nb3Sn superconductors has been quantitatively analyzed using a high-frequency vibrating sample magnetometer, and the results showed that the APC conductors have higher non-Cu J c at high fields (e.g. 32% −41% higher at 16 T) and simultaneously lower non-cu J c (e.,g. 28% −34% lower at 1 T) compared with the RRP® conductor.
Abstract: Nb3Sn superconductors are promising for building accelerator magnets for future energy-frontier circular colliders. A critical factor for this application is the low-field persistent-current magnetization because it leads to several critical issues: e.g. low-field instability (including flux jumps), hysteresis loss, and field errors in magnet bores. Suppression of low-field magnetization requires reduction of low-field critical current density (J c) or effective subelement size (d eff). However, reduction of d eff of state-of-the-art Nb3Sn conductors—the restacked-rod-process (RRP®) type—below 40–50 μm without a pronounced decrease in high-field J c is difficult. On the other hand, the internal oxidation method which forms artificial pinning centers (APC) in Nb3Sn offers an alternative approach to reducing the low-field magnetization. Compared with a conventional Nb3Sn conductor whose flux pinning force versus field (F p–B) curve peaks at ∼20% of its irreversibility field (B irr), the F p–B curve peaks of APC conductors shift to higher fields due to the point pinning effect, leading to flattening of the J c–B curves. The goal of this paper is to quantitatively study how much the APC approach can reduce the low-field magnetization. We measured the J c–B curves of an RRP® conductor and two APC conductors (reacted at 700 °C) from zero field to B irr using a high-field vibrating sample magnetometer. The results showed that the APC conductors have higher non-Cu J c at high fields (e.g. 32%–41% higher at 16 T) and simultaneously lower non-Cu J c at low fields (e.g. 28%–34% lower at 1 T) compared with the RRP®. This effect is due to a competition between their Nb3Sn layer fraction ratios and layer F p ratios. Suppose they reach the same 16 T non-Cu J c, then the 1 T non-Cu J c and magnetization of the APC conductors are only half or even less compared with the RRP® conductor.
1 citations
TL;DR: In this article , MgB2 superconducting bulks with additions of AlB2 powder were prepared and analyzed in an attempt to enhance the critical current density of the material.
Abstract: Optimization of intrinsic and extrinsic properties of MgB2 superconducting material is extremely important for practical application in cables, wires, and tapes. The main mechanisms used to obtain this optimization are through the synthesis process, improvement in the grain connectivity, densification, pinning, doping, and limiting MgO formation. Many groups around the world use elements such as Ti, Zr, Hf, Al, Mn, Si and others, as dopants. Defects or any other inhomogeneity in the superconducting matrix can improve the flux pinning behavior and, hence, the transport properties. In this work MgB2 superconducting bulks with additions of AlB2 powder were prepared and analyzed in an attempt to enhance the critical current density of MgB2 and to understand the effect of this addition on the intrinsic and extrinsic characteristics of the material. Crystallographic, microstructural, optical, and superconducting characterization were performed and analyzed. AlB2 additions modified the superconducting properties of MgB2 increasing its critical current density and irreversibility field compared to pure MgB2 prepared using the same procedures.
22 Mar 2023
TL;DR: In this paper , surface pinning was used as a mechanism for compressing the magnetic flux in the holes of a type-II superconductor, and it was shown that the holes with diameter up to 2 mm are advantageous for bulk single-crystal REBCO samples.
Abstract: Holes drilled in a type-II superconductor trap the magnetic flux. Following Clem's flux pinning model, we consider surface pinning as a mechanism for compressing the magnetic flux in the holes. Estimations of the trapped magnetic flux demonstrate that the holes with the diameter up to 2 mm are advantageous for bulk single-crystal REBCO samples. The REBCO films and tapes can be improved by the holes with diameter smaller than 10 $\mu$m.
TL;DR: In this paper , an artificial superconducting multilayer to act as an alternative approach to study multicomponent superconductivity is presented, where the additional repulsive length and the coupling strength among superconding films were regulated by changing the thickness of the insulting layer.
Abstract: Multicomponent superconductors exhibit nontrivial vortex behaviors due to the various vortex–vortex interactions, including the competing one in the recently proposed type-1.5 superconductor. However, potential candidate that can be used to study the multicomponent superconductivity is rare. Here, we prepared an artificial superconducting multilayer to act as an alternative approach to study multicomponent superconductivity. The additional repulsive length and the coupling strength among superconducting films were regulated by changing the thickness of the insulting layer. The magnetization measurements were performed to clarify the effect of the competition between the repulsive vortex interactions on the macroscopic superconductivity. The vortex phase diagram and the optimum critical current density have been determined. Furthermore, a second magnetization effect is observed, and is attributed to the upper layer, which provides the weak pinning sites to localize the flux lines. The pinning behaviors switches to the mixed type with the increase of the insulting layer thicknesses. Our results open a new perspective to the study and related applications of the multilayer superconducting systems.
TL;DR: The magnetic pinning properties of a ferromagnet/superconductor hybrid structure consisting of a La 0.7Sr0.3MnO3 (LSMO) layer with various thicknesses on top of a fixed thickness YBa2Cu3O7-x (YBCO) layer are investigated in this paper .
Abstract: The magnetic pinning properties of a ferromagnet/superconductor hybrid structure consisting of a La0.7Sr0.3MnO3(LSMO) layer with various thicknesses on top of a fixed thickness YBa2Cu3O7–x (YBCO) layer are investigated in this article. The existence of a weakly magnetic layer was identified at the interface between YBCO and LSMO by a ferromagnetic resonance (FMR) study. Magnetic moment and anisotropy of the interfacial layer were probed using the angular-dependent FMR study. This layer gives rise to an additional flux pinning contribution to the bulk magnetic pinning from the LSMO layer. Our study provides insight into the complex interface physics in the LSMO/YBCO bilayer system, promoting a new pathway for the development of novel flux pinning-related functionality.
TL;DR: In this article , a modified critical current density (Jc) model was proposed to consider r-z plane Jc inhomogeneity, and simulating flux jumps under experimental conditions by solving a 2D axisymmetric electromagnetic-thermal coupled model.
Abstract: In pulsed field magnetization (PFM), the phenomenon of flux jump is capable of driving magnetic flux vortexes into the GdBCO superconducting bulk center to aid full magnetization. Various homogeneous critical current density (J c) models have been implemented to reproduce flux jumps, but the simulated multi-physical responses differ from experimental observations. This paper proposes a modified J c model to consider r–z plane J c inhomogeneity, and simulates flux jumps under experimental conditions by solving a 2D axisymmetric electromagnetic-thermal coupled model. A numerical treatment is developed to reflect the breaking of shielding current during flux jumps. The accuracy of our model is verified by comparisons of the calculated results for trapped magnetic fields (B T) and the PFM and field-cooling experimental results. On this basis, we investigate the improvement of the inhomogeneous J c model and obtain multi-physical responses that show better agreement with the experimental results compared to the homogeneous J c model. Moreover, to further test the ability of the inhomogeneous J c model to predict the anisotropy of the spatial magnetic field distribution, the simulated B T profiles at the top and bottom surfaces of the high-temperature superconductor (HTS) bulk at 77 K are compared to the experiments. This study may provide a new approach for modeling the inhomogeneity of J c characteristics and a useful analysis tool for industrial devices using HTS bulk magnets.
TL;DR: In this paper , the effect of rare earth Gd on the superconducting properties of Nb0.6Ti0.4 and Ta 0.4Ti 0.6 alloys was investigated.
TL;DR: In this paper , the progress made recently in HTS nanocomposites towards controllable generation of APCs with desired morphologies, dimension, concentration, and pinning efficiency for targeted applications is discussed.
Abstract: After theoretical discovery of quantized magnetic vortices in type II superconductors by Abrikosov, which received 2003 Nobel Prize in Physics, vortex pinning has been an important topic of research for high critical current densities in applied magnetic fields desired for a variety of applications in electric and electronic devices and systems. The small vortex core size in high temperature superconductors (HTSs), of a few nanometers, has prompted an intensive research in development of nanoscale artificial pinning centers (APCs) in so-called HTS nanocomposites. Exciting results of much enhanced in-field critical current densities and pinning force densities have been achieved. This talk intends to highlight the progress made recently in HTS nanocomposites towards controllable generation of APCs with desired morphologies, dimension, concentration, and pinning efficiency for targeted applications. The future research in HTS nanocomposites to meet the need of practical applications will also be discussed.
TL;DR: In this article , the superconducting properties of lanthanum films were studied via magnetic and electrical transport measurements and the critical current density (Jc) and vortex-pinning behavior was analyzed.
Abstract: Lanthanum films were grown on the substrate of Si(100) (La/Si(100)) by the molecular beam epitaxy (MBE) method and their superconducting properties were studied via the magnetic and electrical transport measurements. The superconducting transition temperature (Tc) is around 5.3 K. Besides, the second magnetization peak (SMP) occurs well below the upper critical field Hc2(T) due to the thermomagnetic flux-jump instabilities. In addition, we also calculated the critical current density (Jc) and studied the vortex-pinning behavior. The Jc is higher than 10 MA/cm2 at certain temperatures. The pinning analysis suggests the dominant role is the δl pinning. Moreover, the comprehensive superconducting phase diagram is offered. Our study completes the superconducting properties of lanthanum, which would facilitate the understanding of superconducting mechanism in the type Ⅱ superconductors.
TL;DR: The phase separation commonly exists in Fe(Se, Te) and damages their superconducting performance as discussed by the authors , and the phase separation can be tuned by adding FeF2 to the raw materials.
Abstract: The phase separation commonly exists in Fe(Se, Te) and damages their superconducting performance. In this paper, we successfully tuned the phase separation in Fe(Se, Te) via adding FeF2 to the raw materials. A macroscopically ordered phase separation which exhibited submillimetre scale striations in width arranged along the c-axis was formed in the FeF2-added Fe(Se, Te), different from the commonly observed flower shape phase separation in FeF2-free Fe(Se, Te). Moreover, the two macroscopical separated phases were identified as FeSe0.6Te0.4 and FeSe0.4Te0.6. The regular phase separation morphology and the fixed phase composition enhanced the flux pinning behavior which induced the appearance of Δκ pinning and deferred the changing from point pinning to surface pinning with the raising temperature. As a result, Fe(Se, Te) with the macroscopically ordered phase separation overwhelms the common phase separation Fe(Se, Te) in Hc2, U0, and Jc. Notably, at 4.2 K, the critical current density Jc reaches 9.3 × 104 A/cm2 in self-field and 1.3 × 104 A/cm2 at 7 T which outclassed the reported values. Besides, the well-defined stoichiometry of the separated phase also lead to a higher Tc of 15.42 K with a narrower transition width of only 0.98 K. Overall, our work reveals the tuning of phase separation in Fe(Se, Te) in terms of phase morphology and stoichiometry, which is a new strategy for improving the superconducting performance in Fe(Se, Te).
TL;DR: In this paper , the critical currents and pinning mechanisms in single crystals of the high-temperature superconductor Y123 with Mo substituted into CuO chains were investigated and the scaling of the pinning force was performed using the Kramer approach and the Dew-Hughes model.
Abstract: In this work, we investigated the critical currents and pinning mechanisms in single crystals of the high-temperature superconductor Y123 with Mo substituted into CuO chains. The single crystals were annealed in oxygen at low (130–140 atm) and high (255 atm) pressure, which significantly influenced the observed properties. Magnetic hysteresis loops were measured at various temperatures in fields up to 14 T, for both H|| c and H⊥ c. On the basis of these measurements, the densities of critical currents were calculated using the Bean critical state model. Then, using the Kramer approach and the Dew-Hughes model, scaling of the pinning force was performed and the type of pinning centers and pinning mechanisms dominant in different field and temperature ranges were determined. Due to Mo substitution, the critical current density in single crystals annealed in oxygen under high pressure increased several times at lower temperatures, e.g., 3–4 times for T = 4–35 K and [Formula: see text] = 1–8 T, and by an order of magnitude at higher temperatures, e.g., for T = 65–75 K and [Formula: see text] = 2–3 T. For these single crystals, Δκ volume-like pinning centers (Mo2O11 octahedra dimers) and normal point-like pinning centers (interstitial oxygen) were identified as dominant at lower and higher fields, respectively.
TL;DR: In this article , a simple annealing method was applied to tailor flux pinning structures in slightly underdoped BaFe2-xNixAs2 single crystals without significantly compromising superconductivity.
TL;DR: In this paper , the H-ion irradiation of REBCO second generation high temperature superconductor strip was carried out by using the 320kV high charge state ion synthesis research platform.
Abstract: In order to further improve the superconducting current carrying capacity of REBCO coated conductor under strong magnetic field, ion irradiation is used to generate the pinning center of introduced magnetic flux in the REBCO coated conductor. In this paper, the H-ion irradiation of REBCO second generation high temperature superconductor strip was carried out by using the 320kV high charge state ion synthesis research platform. DB-SPBA combined with Raman spectroscopy was used to measure the change of microstructure in YBCO samples irradiated by H+ions within the range of 5.0×1014~1.0×1016. The positron annihilation parameters in YBCO before and after irradiation were analyzed. It is found that after 100 keV H+ion irradiation, a large number of defects including vacancy, vacancy group or dislocation group are produced in the superconducting layer. The larger the irradiation dose, the more vacancy type defects are produced, the more complex the defect types are, and the annihilation mechanism of positrons in the defects changes. Raman spectroscopy results show that with the increase of H+ion irradiation dose, the oxygen atoms in the coating rearrange, the plane spacing increases, the orthogonal phase structure of the coating is destroyed, and the degree of order decreases. The defects produced by such ion irradiation lay a foundation for the introduction of flux pinning centers. Further research can be carried out in combination with X-ray diffractometer, transmission electron microscope, superconductivity and other testing methods to provide theoretical and practical reference for the optimization of material properties.
TL;DR: In this paper , an interface engineering strategy, alternating growth of a 10 nm-thick nonsuperconducting FST seed layer and a 400 nmthick FST superconducting layer, was employed to guarantee the crystalline quality of the films with thicknesses of the order of micrometers, resulting in a highly biaxial texture with grain boundary misorientation angle less than the critical value ∼ 9°.
Abstract: Increasing the thickness of a superconducting layer and simultaneously reducing the thickness effect in iron-based superconducting coated conductors are particularly essential for improving the critical current Ic. Here, for the first time, we have deposited high-performance FeSe0.5Te0.5 (FST) superconducting films up to 2 μm on LaMnO3-buffered metal tapes by pulsed laser deposition. An interface engineering strategy, alternating growth of a 10 nm-thick nonsuperconducting FST seed layer and a 400 nm-thick FST superconducting layer, was employed to guarantee the crystalline quality of the films with thicknesses of the order of micrometers, resulting in a highly biaxial texture with grain boundary misorientation angle less than the critical value θc ∼ 9°. Moreover, the thickness effect, that the critical current density (Jc) shows a clear dependence on thickness as in cuprates, is reduced by the interface engineering. Also, the maximum Jc was found for a 400 nm-thick film with 1.3 MA/cm2 in self-field at 4.2 K and 0.71 MA/cm2 (H∥ab) and 0.50 MA/cm2 (H∥c) at 9 T. Anisotropic Ginzburg-Landau scaling indicates that the major pinning centers vary from correlated to uncorrelated as the film thickness increases, while the thickness effect is most likely related to the weakening of flux pinning by the fluctuation of charge-carrier mean free path (δl) and strengthening of flux pinning caused by the variation of superconducting transition temperature (δTc) due to off-stoichiometry with thickness.
TL;DR: In this article , Zhou et al. showed that there was a correlation between pinned fluxes at volume defects and pinned flux at grain boundaries, and they presented mechanisms of the correlation and details of relative calculations.
Abstract: In order to enhance flux-pinning effect of grain boundaries, we quenched 5 wt% (Fe, Ti) doped MgB2 superconductor in water. During the study, we discovered that there was a correlation between pinned fluxes at volume defects and pinned fluxes at grain boundaries. We present mechanisms of the correlation and details of relative calculations. Pinned fluxes at a volume defect are leak-out-depinned through grain boundaries because grain boundaries are connected to the volume defect. Several equations were derived, which are push-out-depinned force of flux quanta from a volume defect, flux-pinning force of flux quanta at grain boundaries, and the number of leak-out-depinned fluxes from a volume defect. TEM images proved that many grain boundaries would exist on MgB2 grains which are contact on (Fe, Ti) particles. A result was obtained by comparing M–H curve of air-cooled 5 wt% (Fe, Ti) doped MgB2 with that of water-quenched one on the base of the equations, which shows approximately 34% of the number of flux quanta pinned at the volume defect was leak-out-depinned from the volume defect and pinned at the grain boundaries. The study suggested that amount of pinned fluxes at grain boundaries could be calculated by M–H curve of superconductor.
TL;DR: In this article , the peak trapped field was further enhanced to 3.39 T and 3.31 T for the single bulk single grain and the bulk assembly, respectively, by employing a two-step multi-pulse PFM process.
Abstract: The practical magnetization of arrays of multiple single grain, bulk high temperature superconductors is essential for practical applications, such as trapped flux rotating machines, magnetic resonance imaging and nuclear magnetic resonance. We report a systematic investigation of the pulsed field magnetization (PFM) of a bulk assembly consisting of two rectangular Y–Ba–Cu–O bulk single grains, in close proximity, at various temperatures. The measurements of the dynamic variation of the magnetic flux density, supported by numerical analysis, reveal that the induced screening currents during the rise of a pulsed field may greatly enhance the flux density in the region of the junction leading to uneven flux penetration and to an increased likelihood of flux jumps in this region. Such coupling between field and current promotes magnetic flux penetration and improves the peak trapped field from 3.01 T for a bulk single grain to 3.11 T for the bulk assembly at 30 K, improving the magnetization efficiency from 80% to 90%. The peak trapped field was further enhanced to 3.39 T and 3.31 T for the single bulk single grain and the bulk assembly, respectively, by employing a two-step multi-pulse PFM process.
04 Jun 2023
TL;DR: In this article , a travelling wave flux pump is used to accurately output industrial-scale DC current into high-temperature superconducting (HTS) magnets, which demonstrates that the DC current of the flux pump originates from the motional electromotive force other than the induced e.m.f., and applying different strengths of DC fields can modulate the magnitude of the output current.
Abstract: Understanding and controlling the motion of superconducting vortices has been a key issue in condensed matter physics and applied superconductivity. Here we present a method for macroscopically manipulating the vortices based on travelling wave flux pump to accurately output industrial-scale DC current into high-temperature superconducting (HTS) magnets. DC magnetic fields are used to adjust the polarity of the vortices and thus modulate the direction of the output current, which demonstrates that the DC current of the flux pump originates from the motional electromotive force ( e.m.f. ) other than the induced e.m.f.. In addition, applying different strengths of DC fields can modulate the magnitude of the output current. Further numerical simulation suggests how the flux inside the superconducting tape is controlled by different applied fields. We build a controlled flux flow model to correctly explain the behavior of vortices controlled by the flux pump, and how the motional e.m.f. is created by manipulating the vortices. Based on the method, we achieve high precision regulation of output current using adaptive control of the DC magnetic field, allowing the flux pump to output DC current just as accurate as a typical commercial power supply. This work advances the technic for macroscopic manipulation of vortices.
TL;DR: In this article , the effect of Ca doped YBCO space layers in the multilayer composite film, on the BZO nanorod/YBCO interface, over a wide range of conditions of 65 − 5 K and 0 − 9 T, was presented.
Abstract: An important research goal in the applications of high temperature superconductor YBa 2 Cu 3 O 7-δ (YBCO) thin films is increasing both the critical current density and also the isotropic nature of the film. YBCO is inherently anisotropic due to its layered perovskite structure. The critical current density of YBCO thin films is enhanced by increasing the flux pinning sites in the film by the addition of insulating nano-phase materials, such as BaZrO 3 (BZO) nanorods, which are also anisotropic in nature. Using a multilayer pulsed laser deposition technique has been shown to produce films with inclusions that are more isotropic in nature. However, the defective BZO nanorod interface, resulting from its lattice mismatch with YBCO, prevents obtaining optimum pinning force. This research explores the effect of Ca doped YBCO space layers in the multilayer composite film, on the BZO nanorod/YBCO interface, over a wide range of conditions of 65–5 K and 0– 9T that are suitable for various applications. The interplay of combining these three variables: BaZrO 3 addition to YBCO, multilayer film growth resulting from varying pulsed laser deposition conditions, and employing calcium doped YBCO space layers, and the resulting impact on film microstructures and superconducting properties, will be presented.