Jc In Magnetic Fields Research Articles

Enhancement of critical current densities by co-doping with Zr, Sn and Ce for Gd123 thin films fabricated by fluorine-free MOD method

Abstract We have fabricated GdBa2Cu3O7-δ thin films co-doped several types of BaMO3 (M=Zr, Sn, Ce) artificial pinning centers with different lattice constants and Young’s modulus from 2.0 to 5.0 mol% on LaAlO3 single crystal substrates by the FF-MOD method. When several types of BaMO3 are simultaneously introduced into Gd123 films by the FF-MOD method, Ba required for BaMO3 crystal growth is shared among them, each crystal growth is suppressed, and thus the crystals become finer and denser. This resulted in a remarkable enhancement of the critical current densities in magnetic fields. The maximum J c of 16.57 MA cm-2 at 0 T and 1.97 MA cm-2 at 3.0 T, 30 K obtained for the Gd123 film introduced three types of BaMO3 (M=Zr, Sn, Ce) with 4.0 mol% were 1.22 and 1.76 times larger than those for the film with the same amount of BaCeO3. This method shows a new strategy to improve Jc in magnetic fields of REBCO.

Effect of 1.5 MeV Proton Irradiation on Superconductivity in FeSe0.5Te0.5 Thin Films

Raising the critical current density Jc in magnetic fields is crucial to applications such as rotation machines, generators for wind turbines and magnet use in medical imaging machines. The increase in Jc has been achieved by introducing structural defects including precipitates and vacancies. Recently, a low-energy ion irradiation has been revisited as a practically feasible approach to create nanoscale defects, resulting in an increase in Jc in magnetic fields. In this paper, we report the effect of proton irradiation with 1.5 MeV on superconducting properties of iron–chalcogenide FeSe0.5Te0.5 films through the transport and magnetization measurements. The 1.5 MeV proton irradiation with 1 × 1016 p/cm2 yields the highest Jc increase, approximately 30% at 5–10 K and below 1 T without any reduction in Tc. These results indicate that 1.5 MeV proton irradiations could be a practical tool to enhance the performance of iron-based superconducting tapes under magnetic fields.

Effects of Sm1+xBa2-xCu3Oy Films with Non-Stoichiometric Composition Fabricated by Combinatorial Pulsed Laser Deposition method on the Superconducting Properties

Sm1+xBa2-xCu3Oy, (Sm-rich) had higher critical current density (Jc) in magnetic fields and higher irreversible fields than stoichiometric SmBa2Cu3Oy (SmBCO) thin films. In this study, to clarify the features of artificial pinning centers (APCs) doped Sm-rich films, we prepared BaHfO3 (BHO)-doped Sm1+xBa2-xCu3Oy films with x = 0.00 ∼ 0.20 using combinatorial pulsed laser deposition (C-PLD) method on a metallic substrate and we evaluate surface morphrogies, crystal orientations and superconducting properties of the films. As a result, when x increased, the terrace width also increased. From the measurement of Jc in magnetic fields, the BHO-doped Sm-rich films showed Jc plateaus around 1 ∼ 3 T. From the angulaer dependence of Jc, the BHO-doped Sm-rich films showed Jc peak where B is parallel to c-axis. From several measurements, we discuss effects of Sm1+xBa2-xCu3Oy films with and without BHO on the superconducting properties.

Control of in-field performance of 25 mol.% Zr-added REBCO superconductor tapes

The relation between the c-axis lattice parameter of REBa2Cu3O7−δ (REBCO and RE = Gd, Y) superconductors with 25 mol.% Zr addition and the critical current density (Jc) was determined at (77 K, 0 T), (30 K, 3 T (B||c)), and (30 K, 9 T (B||c)). In this work, heavily doped Zr-added REBCO films with the thickness of 0.9 µm were fabricated by metal organic chemical vapor deposition (MOCVD) using a roll-to roll process. An increase in REBCO c-axis lattice parameter and a decrease in elastic mismatch strain relative to self-assembled BZO nanocolumns were observed with increasing (Ba + Zr)/Cu content. The optimum c-axis lattice parameter for achieving the highest Jc in magnetic field was found to be temperature and field dependent, with optimum values of 11.74, 11.76 and 11.78 Å at (77 K, 0 T), (30 K, 3 T (B||c)), and (30 K, 9 T (B||c)), respectively.

C-axis correlated pinning mechanism in vortex liquid and solid phases for Sm123 film with well-aligned BaHfO3 nanorods

Nanorods, which are nano-scaled columnar-shape precipitates, have recently been used to improve critical current density Jc in magnetic fields for REBa2Cu3Oy (RE123, RE: rare earth element) high temperature superconducting tapes/films. However, the flux pinning mechanism of the nanorod is not clear yet. We investigated the Jc and resistivity ρ properties in detail and discussed the flux pinning properties on the basis of the flux pinning state diagram for high-quality Sm123 films with well-aligned 5.6 vol% BaHfO3 nanorods. Plateaus were observed in the field dependence of Jc and ρ at high temperatures above the delocalization temperature. This suggests that nanorod pinning becomes effective in the vortex liquid phase and it grows up when the temperature decreases toward the delocalization temperature. In the ‘many-nanorod’ state in the high temperature region above the delocalization temperature, double peaks in the Fp curves appear due to the coexistence of nanorod pinning and random pinning. At low temperatures below 70 K, however, the well-scaled Fp curves at low fields and temperature dependent (non-scaled) normalized Fp curves are observed. From detailed analysis using the cooperation model of the random and the correlated pinning centers, we found that nanorod pinning is dominant below the matching field and the cooperation between nanorod pinning and random pinning determines the high field Jc properties above the matching field.

Miniaturization of BaHfO3 nanoparticles in YBa2Cu3Oy-coated conductors using a two-step heating process in the TFA-MOD method

The critical current density (Jc) of YBa2Cu3Oy (YBCO)-coated conductors in a magnetic field can be enhanced by the doping of flux-pinning centers in a metal organic deposition (MOD) process with trifluoroacetates (TFA). The size of these flux-pinning centers should be less than 10 nm to achieve commercial use due to the coherence length of YBCO at 77 K. In this paper, BaHfO3 (BHO) nanoparticles were introduced into YBCO films using the TFA-MOD method. Microstructures and the Jc properties of the films prepared using a two-step heating process at crystallization were compared with film prepared using a conventional one-step heating process. The two-step heating process produced 15 nm average-sized BHO nanoparticles in the film compared to 19 nm nanoparticles in a film prepared using a one-step process. It was revealed that the size of nanoparticles in the films could be miniaturized by improving the heating processes in the MOD method, and the miniaturized nanoparticles could contribute to increased Jc in magnetic fields. The mechanism of miniaturization is also discussed based on microstructure observations of quenched films.

Viewpoint on fast track communication by Z Gao et al ‘high transport Jc in magnetic fields up to 28 T of stainless steel/Ag double sheathed Ba122 tapes fabricated by scalable rolling process’

Viewpoint on fast track communication by Z Gao et al ‘high transport Jc in magnetic fields up to 28 T of stainless steel/Ag double sheathed Ba122 tapes fabricated by scalable rolling process’

シード層を導入したIBAD-MgO 基板上 BaHfO<sub>3 </sub>添加SmBa<sub>2</sub>Cu<sub>3</sub>O<i><sub>y </sub></i>薄膜の臨界電流密度向上

The development of rare earth (RE) Ba2Cu3Oy (REBCO) coated conductors has been carried out by many groups. The critical current density (Jc) in high magnetic fields needs to be improved for superconducting applications. We have fabricated BaHfO3 (BHO)-doped SmBa2Cu3Oy films on ion beam-assisted deposition (IBAD)-MgO substrates using pulsed laser deposition (PLD). In this study, we introduce a seed layer technique. As a result, the appropriate growth temperature (Ts) is expanded to higher temperature range without BaCeO3 outgrowth around the interface of the SmBCO and CeO2 cap-layer. We were able to control the configurations of the BHO nanorods within the SmBCO films as compared to the conventional PLD method. The SmBCO + BHO (1.4 vol.%) films, which were fabricated at a Tsupper of 900ºC, showed that the Jc in the magnetic field (B // c) was improved as compared to pure-SmBCO films. Furthermore, the global pinning force density reached 21 GN/m-3 at 77 K in B = 2 T.

High transport Jc in magnetic fields up to 28 T of stainless steel/Ag double sheathed Ba122 tapes fabricated by scalable rolling process

The recently discovered iron-based superconductors with very high upper critical field (Hc2) and small anisotropy have been regarded as a potential candidate material for high field applications. However, enhancements of superconducting properties are still needed to boost the successful use of iron-based superconductors in such applications. Here, we propose a new sheath architecture of stainless steel (SS)/Ag double sheath and investigate its influence on the microstructures and Jc-H property. We found that the transport Jc-H curves for rolled and pressed tapes both show extremely small magnetic field dependence and exceed 3 × 104 A cm−2 under 28 T, which are much higher than those of low-temperature superconductors. More interestingly, 12 cm long rolled tape shows very high homogeneity and sustains Jc as high as 7.7 × 104 A cm−2 at 10 T. These are the highest values reported so far for iron-based superconducting wires fabricated by scalable rolling process. The microstructure investigations indicate that such high Jc was achieved by higher density of the core and uniform deformation resulting better texturing. These results indicate that our process is very promising for fabricating long Ba122 wires for high field magnet, i.e. above 20 T.

Systematic change of flux pinning in (Dy,RE)123 and (Y,RE)123 melt-solidified bulks with unit cell orthorhombicity

RE-mixing is one of the most effective ways to enhance critical current density Jc of RE123 melt-solidified bulks; however, the intrinsic effects of RE-mixing on Jc have not yet been well clarified. Through synthesis and analysis of eight types of melt-solidified bulks containing one or two RE elements, the effects of RE-mixing on Jc-H characteristics were systematically investigated. It was revealed that RE-mixed bulks show higher Jc than RE123 bulks accompanied by the secondary peaks of Jc in a high field region. Analyses on the relationship between Jc and orthorhombicity suggested that the RE substitution level for Ba sites can be controlled by RE-mixing to enhance Jc in magnetic fields. Combined with the results of magnetic measurements at 40 and 60 K up to 15 T, RE-mixed bulks originating from Y123 powders were found to be high potential materials for high field generating applications.

Flux Pinning Properties and Microstructures of Multilayered Films Consisting of Sm1.04Ba1.96Cu3Oy Layers and BaSnO3-Doped Sm1.04Ba1.96Cu3Oy Layers

In order to enhance Jc in magnetic fields for all applied angles, we fabricated multilayered films consisting of Sm1.04Ba1.96Cu3Oy (SmBCO) layers and BaSnO3 (BSO)-doped SmBCO layers on MgO substrates (multilayered SmBCO) by the pulsed laser deposition (PLD) method. We varied the numbers of layers (8, 16, 32, and 64). In the magnetic field angle dependence of Jc (B = 1 T, 77 K), only in the 8-layer sample was Jc higher than that of pure SmBCO thin films for all applied angles. The other sample showed different Jc characteristics.

High critical current density and its magnetic fields dependence in (Sm,Eu,Gd)Ba2Cu3Oy films by using multiple targets

Melt textured bulks of (Sm0.33Eu0.33Gd0.33)Ba2Cu3Oy (SEG123) show high Jc compared with that of YBa2Cu3Oy (Y123), because of nanoscopic network consisting of crossing rare earth (RE) compositional stripes. In this study, we fabricated SEG123 films by using pulsed laser deposition (PLD) method on LaAlO3 (LAO) substrates and evaluated the Jc and Tc in magnetic field. Jc of the SEG123 film was typically 1.4MA/cm2 at 77K in self-field. Jc in self-field of SEG123, Y123 and Sm123 films were almost the same value, however, Jc in magnetic fields showed a notable difference. The Jc of SEG123 film were 62.7kA/cm2 at 5T. We conclude that the Jc in magnetic fields were improved by RE-rich particle made of RE/Ba substitution acting as 3-dimensional pinning centers. Moreover we have confirmed that the superconducting properties changes by varying Sm, Eu and Gd composition ratio.

Possibility of Nd:YAG-PLD Method for Fabricating REBCO Coated Conductors

A Nd:YAG (neodymium-doped yttrium aluminum garnet) laser is environmentally safe, due to the absence of any poisonous or hazardous gases, and also economical, without the need for expensive gases. We can thus expect a safe and low cost <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\rm REBa}_{2}{\rm Cu}_{3}{\rm O}_{y}$</tex> </formula> (REBCO)-coated conductor fabrication process by using an Nd:YAG laser. We investigated the fabrication of <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\rm YBa}_{2}{\rm Cu}_{3}{\rm O}_{y}$</tex></formula> (YBCO) films using a PLD method with a fourth harmonic Nd:YAG laser. The YBCO films showed good superconducting properties; for example, on <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex Notation="TeX">${\rm SrTiO}_{3}$</tex></formula> single crystalline substrates, <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$T_{\rm c}$</tex></formula> and <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$J_{\rm c}$</tex></formula> were about 90 K and 2.5 <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\rm MA/cm}^{2}$</tex></formula> , respectively, at 77 K. In order to enhance <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$J_{\rm c}$</tex></formula> in magnetic fields, <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\rm BaSnO}_{3}$</tex> </formula> was doped into YBCO films by means of a combinatorial Nd:YAG-PLD method. The combinatorial method enabled the growth and study of a library of samples ranging from pure-YBCO to BSO-doped-YBCO. We demonstrated rapid optimization of <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\rm BaSnO}_{3}$</tex> </formula> content by the combinatorial method and concluded that the optimal BSO content was around 3.6 wt%. In addition, in order to enhance material yield of the Nd:YAG-PLD method, we optimized the oxygen pressure and distance between the target and substrate. On a substrate with dimensions of <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$10\times 10\ {\rm mm}^{2}$</tex> </formula> , the material yield of a YBCO film reached about 19.0%. These results suggest that the Nd:YAG-PLD method is promising for forming YBCO-coated conductors.

Effects of tin-compounds addition on Jc and microstructure for YBCO films

Tin-compounds were doped into YBa2Cu3O7−δ (YBCO) films as pinning centers to enhance Jc in magnetic fields. YBCO films were grown by a metal organic deposition process using tri-fluoroacetates starting solutions. Tin-acetylacetonate salts were then dissolved into the starting solution as pinning centers. Jc of the YBCO films with tin-acetylacetonates were enhanced in all magnetic field angles. Transmission electron microscopy (TEM) and TEM-EDS (Energy Dispersive X-ray Spectroscopy) observations revealed the existence of tin-compound particles with the size of about 30nm in the YBCO film. These nano particles were distributed randomly in the film and were considered to act as 3-dimentional pinning centers.

Effect of single-walled carbon nano-tube (CNT) addition on superconducting properties of bulk MgB2 superconductor

Here, effect of single-walled carbon nano-tube (CNT) doping on transition temperature, lattice parameters, critical current density and flux pinning in MgB2 superconductor was studied. The carbon substitution for B was found to enhance critical current density Jc in magnetic fields but depress critical temperature Tc. The depression of Tc is caused by the carbon substitution for B, which is also confirmed by Rietveld analysis of room temperature XRD patterns of doped samples. We achieved enhancement of critical current density (Jc) and flux pinning by almost an order of magnitude, particularly in higher magnetic fields.

Progress towards nanostructured SmBCO film for controlling pinning properties

We have studied the artificial pinning center (APC) techniques in Sm1+xBa2-xCu3Oy (SmBCO) films deposited on single crystalline substrates. As a result, using the Low Temperature Growth (LTG)-PLD technique, Jc of 0.28 MA/cm2 at 77 K, B=5 T (B // c) was obtained on 700 nm thick SmBCO films grown on 50 nm thick SmBCO-seed bufferd MgO substrate. Following the successful demonstration of the growth of SmBCO films on single crystalline substrate, the LTG technique was also extended to coated conductor on metal substrates. With the objectives of applying the superconducting magnetic application that operate at liquid nitrogen temperature, we report the Jc in magnetic field and the microstructure of SmBCO coated conductor. PLD-SmBCO with a Jc of over 0.1 MA/cm2 at 5 T (B // c, 77K) were grown on IBAD-YSZ/CeO2 tape, which is higher than YBCO/IBAD. In addition, the Jc values of the SmBCO coated conductor grown with LTG technique measuring 0.23 MA/cm2 for 5 T of B // c at 77 K are comparable to that of NbTi for 5 T at 4.2 K. From the magnetic field angular dependences of Jc, the anisotropy of the SmBCO film/IBAD tape is small. This performance in SmBCO coated conductor on metal substrate is comparable to the best results of SmBCO films on MgO single crystalline substrates.

Enhancement of Jc in MgB2 thin films on Si substrate with pinning centers introduced by deposition in O2 atmosphere

As-grown MgB2 thin films on Si substrates with high Jc under magnetic fields were prepared by electron-beam evaporation. The value of Jc has been enhanced by the deposition of MgB2 thin film in an O2 atmosphere. The MgB2 thin film deposited in the O2 atmosphere (O2-doped film) has exhibited considerably higher Jc in magnetic fields among MgB2 thin films reported before. It has been found that the high Jc of the O2-doped film is attributable to the flux pinning with grain boundaries strengthened by an introduction of MgO along grain boundaries. In a high magnetic field, a peculiar behavior of E-J characteristics where E-J curves vary in two stages was observed. This behavior also originates from the flux pinning with strengthened grain boundaries.

Enhanced superconducting performances in nanostructured SmBCO coated conductor

We have studied the artificial pinning center (APC) techniques in Sm1+xBa2−xCu3Oy (SmBCO) films deposited on single crystalline substrates. As a result, using the low temperature growth (LTG)-PLD technique, Jc of 0.28 MA/cm2 at 77K, B=5T (B∥c) was obtained on 700nm thick SmBCO films grown on 50nm thick SmBCO-seed buffered MgO substrate. Following the successful demonstration of the growth of SmBCO films on single crystalline substrate, the LTG technique was also extended to coated conductor on metal substrates. With the objectives of applying the superconducting magnetic application that operate at liquid nitrogen temperature, we report the Jc in magnetic field and the microstructure of SmBCO coated conductor. PLD-SmBCO with a Jc of over 0.1MA/cm2 at 5T (B∥c, 77K) were grown on IBAD-YSZ/CeO2 tape, which is higher than YBCO/IBAD. In addition, the Jc values of the SmBCO coated conductor grown with LTG technique measuring 0.23MA/m2 for 5T of B∥c at 77K are comparable to that of NbTi for 5T at 4.2K. From the magnetic field angular dependences of Jc, the anisotropy of the SmBCO film/IBAD tape is small. This performance in SmBCO coated conductor on metal substrate is comparable to the best results of SmBCO films on MgO single crystalline substrates. We discussed about the elemental mapping of the high-Jc SmBCO coated conductor measured by TEM-EDX.

ＬＴＧ法を用いて作製したＳｍ１＋ｘＢａ２−ｘＣｕ３Ｏｙ薄膜の配向性と成長様式

We have reported high-Jc Sm1+xBa2-xCu3Oy (SmBCO) films prepared by a low-temperature growth (LTG) technique. Despite the low-substrate temperature, the LTG-SmBCO films showed complete c-axis orientation and cube-on-cube texture. In addition, the LTG-SmBCO films showed a Jc of 0.28 MA/cm2 (77 K, B//c, B=5 T), because these included high-dislocation densities and nanosize low-Tc particles. In this study, we discuss the mechanism of c-axis orientation and crystal growth for high-Jc LTG-SmBCO films. We newly suggest a model for “Nucleated growth on c-axis oriented Seed layer (NCS)" to understand the c-axis orientation mechanism for LTG-SmBCO films. Based on the NCS model, when the LTG-SmBCO films nucleated on a seed layer have two-dimensional (2D) nuclei with a 1 unit SmBCO step cell height, the interfacial energy between the nucleus and the seed layer and the critical Gibbs free energy of the nucleus are lower than those of PLD-SmBCO films. Therefore, the LTG-SmBCO films show high crystal quality and a wide processing window for biaxial orientation. We suggest that the LTG technique is effective for not only increasing Jc in magnetic fields, but also improving the processing window and crystal quality.

Magnetic field dependence of critical currents in PLD RE–Ba–Cu–O (RE = Er, Dy, Gd) film prepared on CeO2 capped IBAD-GZO layers

We have fabricated RE1Ba2Cu3O7−δ (RE=Er,Dy,Gd) and YBa2Cu3O7−δ (Y-123) superconductor films with various thickness on pulsed laser deposition (PLD)-CeO2/ion-beam assisted deposition (IBAD)-Gd–Zr–oxide (GZO)/metal substrates by PLD method and investigated the dependence of critical current density (Jc) on applied magnetic field. In order to fabricate a practical high critical current (Ic) coated conductor, we used metal substrate tapes with Δϕ value of 3.7°–7.0° fabricated by the technique of a self-epitaxy method. GdBa2Cu3O7−δ (Gd-123) films showed higher Jc in magnetic fields than that for Y-123 films. Jc value of the Gd-123 film was 179,000A/cm2 at 3T and 34,700A/cm2 at 6T at 77K. Transmission electron microscope (TEM) observation showed that Gd-123 film had a more defective structure than Y-123 film. These structures may be attributed to high Jc in high magnetic field.