High Irreversibility Field Research Articles

Optimisation of pulsed laser deposited Ba1-xKxBiO3 thin films with tunable superconducting properties by control of K doping level, x

The mid-TC superconductor Ba1-XKXBiO3 (BKBO) exhibits different superconducting mechanisms depending on x, in the range ∼ 0.35–0.65. The optimal doping for the highest TC is reported to be around x = 0.4. To understand more about the dependence of the superconducting mechanism on x, high quality and reproducible epitaxial films with controlled x are needed. This has been challenging owing to the volatility of K and (to a lesser extent) Bi. In this work, we use pulsed laser deposition (PLD) with several novel process steps to achieve high-quality films in a reproducible way. These include a modified method for target preparation, a low NO2 growth pressure, and precise positioning of substrates in the PLD plume. Optimum TC films (32 K onset) were grown from an x = 0.4 target, i.e. with no excess K, as is normally used. Stable, higher K content films (made from an x = 0.45 target), were also grown. These x = 0.45 films had a lower TC (22.5 K onset), as expected for (K) overdoped films, with very high upper critical field, HC2 (0 K), and irreversibility field, Hirr (0 K), values, from linear extrapolation, of ∼ 31.7 T and ∼ 28.8 T, respectively. The growth methodology demonstrated in this work is highly beneficial for fundamental mechanistic studies of this complex superconductor on which there is renewed interest, and where controlled compositions and crystalline quality are currently limited.

Key factor for low anisotropy and high irreversibility field in (Cu,C)Ba2Ca3Cu4O11+δ

In cuprate superconductors, the Hg-, Tl- and Bi-based systems with multilayers of CuO2 planes within one unit cell usually have critical temperatures higher than 100 K. However, the applications of these materials under high magnetic fields in liquid nitrogen temperature region are strongly limited by the very high anisotropy and strong vortex motion. The observation of an unprecedented high irreversibility field and low anisotropy in (Cu,C)Ba2Ca3Cu4O11+δ with Tc = 116 K was an exception, and the reason remains elusive. Here, we report the investigations on (Cu,C)Ba2Ca3Cu4O11+δ single crystals. The angle-dependent resistivity under different temperatures and magnetic fields reveals clear evidence of lower anisotropy and higher irreversibility fields. The high resolution scanning transmission electron microscopy allows to clearly visualize that CuO chains and CO chains are formed alternatively at the places where the heavy metal oxides would locate. First-principle calculations confirm that the newly formed CuO chains in the charge reservoir blocks significantly enhance the c-axis coherent electronic conduction, lower the anisotropy and strengthen the irreversibility field. This discovery may be extended in a general sense to other layered cuprates and stimulate high power applications of cuprate superconductors in liquid nitrogen temperature region.

Thermoelectricity and electronic correlation enhancement in FeS by light Se doping

We report thermoelectric studies of FeS$_{1-x}$Se$_x$ ($x$ = 0, 0.06) superconducting single crystals that feature high irreversibility fields and critical current density $J_c$ comparable to materials with much higher superconducting critical temperatures ($T_c$'s). The ratio of $T_c$ to the Fermi temperature $T_F$ is very small indicating weak electronic correlations. With a slight selenium substitution on sulfur site in FeS both $T_c$/$T_F$ and the effective mass $m^*$ rise considerably, implying increase in electronic correlation of the bulk conducting states. The first-principle calculations show rise of the density of states at the Fermi level in FeS$_{0.94}$Se$_{0.06}$ when compared to FeS which is related not only to Fe but also to chalcogen-derived electronic states.

Transport current and magnetization of Bi-2212 wires above liquid Helium temperature for cryogen-free applications

Since the discovery of high temperature superconductors, a possible cryogen-free scenario has always been wished. Nowadays, liquid Helium is running out, and it is likely that the cooling by will be a large part of the costs of any superconducting system. Bi-2212 wires at temperature higher than 4.2 K still show a very high irreversibility field and thus a deep investigation of their properties in such a range of temperature is very useful in order to assess the applicability in high field cryogen-free magnets. Here electrical transport and magnetic properties characterization at variable temperature and magnetic field on our “GDG—processed” wires are reported together with a well-described original approach to calculate the irreversibility field Hirr. This study is devoted to provide reference data on the behaviour of the only isotropic wire for high field application with an eye to the performances at temperatures above 4.2 K.

High temperature superconducting material based energy storage for solar-wind hybrid generating systems for fluctuating power management

The green energy infrastructure plays an important part in existing world of power scarcity. Owing to their dependence on environmental factors, renewable energy technologies continue to fluctuate. Using the energy storage device will solve the problem. The technical and economical requirements of the energy storage process can be met with the use of hybrid combinations. This paper proposes a hybrid energy management system based on the Super conductive magnetic material and the lead acid battery to provide power stabilization in the grid-connected unstable microgrid. Here, second-generation High Temperature Superconducting (HTS) material is used as Super Conducting Magnet Energy Storage (HTSMES) which exhibits a high irreversibility field and critical current density within an active magnetic field. The proposed system may be a good solution to minimize the impact of the Point of Common Coupling (PCC) power variability during fault condition. To improve the efficiency and flexibility of the proposed system, the two hybrid power sources are connected via dual input single output zeta converter. The HTSMES is used to minimize the difference in active power during fault and to give the reactive current to handle the fault. Grid connected microgrid with HTSMES-battery was simulated using the MATLAB Simulink platform and tested using an energy management algorithm with and without the presence of fault. The system proposed is demonstrated with detailed simulation results.

Secondary phase particles in bulk, infiltration-growth processed YBCO investigated by transmission Kikuchi diffraction and TEM

We present results of the first application of the transmission Kikuchi diffraction (TKD) technique to bulk, infiltration growth (IG)-processed YBa2Cu3O7−δ (YBCO) superconductors with embedded Y2BaCuO5(Y-211) nanoparticles. By means of focused ion-beam (FIB) milling, TEM slices were prepared from mechanically polished surfaces of bulk, IG-processed YBCO samples. The required optical transparency was reached by additional polishing the resulting surfaces using the FIB and Ar-ion milling. For TKD, the sample was mounted on a homebuilt sample holder in the SEM, which provides the required inclination for TKD. The improved spatial resolution of TKD enabled the investigation of the small Y-211 particles (diameter of about 60–210 nm) embedded in the superconducting YBCO matrix. The fabricated TEM slices further enable the application of transmission electron microscopy to the same sample sections. These tiny Y-211 particles embedded within the YBCO matrix are, together with their strain fields, directly responsible for the high irreversibility fields due to the effective flux pinning of the IG-processed samples.

Self-intermetallic α-Mn a spin glass by Fe and Al doping: transport study of the α-Mn structure type alloys

In view of the many potential benefits for antiferromagnetic spintronic devices, we investigated the magneto-transport properties of the self-intermetallic α-Mn through Fe and Al doping. Epitaxial α-Mn structure type alloy films consisting of Mn, Fe, and Al were grown on a MgO(001) substrate by molecular beam epitaxy. We used zero-field- and field-cooling Hall resistivity and magnetoresistance measurements of the films to reveal a spin-glass transition at low temperature. The films also exhibited high-field irreversibility and shifted hysteresis loops after field cooling below their freezing temperature. The above observations indicate spin-glass behavior in this system, which might be triggered by magnetic frustration owing to competing antiferromagnetic and ferromagnetic interactions and magnetic site disorder.

Beneficial Impact of Excess Mg on Flux Pinning in Bulk MgB2 Synthesized with Ag Addition and Carbon Encapsulated Boron

Silver addition has been known to improve mechanical and superconducting performance of bulk magnesium boride (MgB2) superconductor synthesized via solid state sintering. While formation of pinning phases and impurities such as Ag–Mg phases and MgO, respectively, responsible for high performance, part of the Mg in initial mixture will be expected to be consumed by silver. In this work, the authors add varied amounts of Mg systematically such as x: 2 (while x = 1.05, 1.075, 1.1, 1.125, 1.15) ratio of Mg:B instead of usual stoichiometric ratio of 1:2. To obtain high superconducting properties, the authors use carbon encapsulated boron (1.5% carbon) along with 4 wt% Ag. X‐ray diffraction analysis shows the presence of Ag–Mg phases and minute amount of MgO. Superconducting quantum interference device (SQUID) measurements indicate that high irreversibility field (4.76 T) and large Jc of 520, 440, and 347 kA cm−2 at 10, 15, and 20 K, respectively, at self‐field was exhibited in sample with x = 1.075. Flux pinning force studies are done to analyze the effect of secondary phases formed. All results analyzed explain the improved critical current performance based on nanometer‐sized Ag–Mg particles in the final product.

Erratum to: Irreversibility Line Measurement and Vortex Dynamics in High Magnetic Fields in Ni- and Co-Doped Iron Pnictide Bulk Superconductors

The de-pinning or irreversibility lines were determined by ac susceptibility, magnetization, radio-frequency proximity detector oscillator (PDO), and resistivity methods in Ba(Fe0.92Co0.08)2As2 ( T c = 23.2 K), Ba(Fe0.95Ni0.05)2As2 ( T c = 20.4 K), and Ba(Fe0.94Ni0.06)2As2 ( T c = 18.5 K) bulk superconductors in ac, dc, and pulsed magnetic fields up to 65 T. A new method of extracting the irreversibility fields from the radio-frequency proximity detector oscillator induction technique is described. Wide temperature broadening of the irreversibility lines, for any given combination of ac and dc fields, is dependent on the time frame of measurement. Increasing the magnetic field sweep rate (dH/dt) shifts the irreversibility lines to higher temperatures up to about dH/d t = 40,000 Oe/s; for higher dH/dt, there is little impact on the irreversibility line. There is an excellent data match between the irreversibility fields obtained from magnetization hysteresis loops, PDO, and ac susceptibility measurements, but not from resistivity measurements in these materials. Lower critical field vs. temperature phase diagrams are measured. Their very low values near 0 T indicate that these materials are in mixed state in nonzero magnetic fields, and yet the strength of the vortex pinning enables very high irreversibility fields, as high as 51 T at 1.5 K for the Ba(Fe0.92Co0.08)2As2 polycrystalline sample, showing a promise for liquid helium temperature applications.

2G HTS wires made on 30 μm thick Hastelloy substrate

REBCO (RE = rare earth) based high temperature superconducting (HTS) wires are now being utilized for the development of electric and electromagnetic devices for various industrial, scientific and medical applications. In the last several years, the increasing efforts in using the so-called second generation (2G) HTS wires for some of the applications require a further increase in their engineering current density (Je). The applications are those typically related to high magnetic fields where the higher Je of a REBCO wire, in addition to its higher irreversibility fields and higher mechanical strength, is already a major advantage over other superconducting wires. An effective way to increase the Je is to decrease the total thickness of a wire, for which using a thinner substrate becomes an obvious and attractive approach. By using our IBAD-MOCVD (ion beam assisted deposition-metal organic chemical vapor deposition) technology we have successfully made 2G HTS wires using a Hastelloy® C276 substrate that is only 30 μm in thickness. By using this thinner substrate instead of the typical 50 μm thick substrate and with a same critical current (Ic), the Je of a wire can be increased by 30% to 45% depending on the copper stabilizer thickness. In this paper, we report the fabrication and characterization of the 2G HTS wires made on the 30 μm thick Hastelloy® C276 substrate. It was shown that with the optimization in the processing protocol, the surface of the thinner Hastelloy® C276 substrate can be readily electropolished to the quality needed for the deposition of the buffer stack. Same in the architecture as that on the standard 50 μm thick substrate, the buffer stack made on the 30 μm thick substrate showed an in-plane texture with a Δϕ of around 6.7° in the LaMnO3 cap layer. Low-temperature in-field transport measurement results suggest that the wires on the thinner substrate had achieved equivalent superconducting performance, most importantly the Ic, as those on the 50 μm thick substrate. It is expected the 2G HTS wires made on the 30 μm thick Hastelloy® C276 substrate, the thinnest and with the highest Je to date, will greatly benefit such applications as high field magnets and high current cables.

Tunable High-Field Magnetization in Strongly Exchange-Coupled Freestanding Co/CoO Core/Shell Coaxial Nanowires.

The exchange bias properties of Co/CoO coaxial core/shell nanowires were investigated with cooling and applied fields perpendicular to the wire axis. This configuration leads to unexpected exchange-bias effects. First, the magnetization value at high fields is found to depend on the field-cooling conditions. This effect arises from the competition between the magnetic anisotropy and the Zeeman energies for cooling fields perpendicular to the wire axis. This allows imprinting predefined magnetization states to the antiferromagnetic (AFM) shell, as corroborated by micromagnetic simulations. Second, the system exhibits a high-field magnetic irreversibility, leading to open hysteresis loops attributed to the AFM easy axis reorientation during the reversal (effect similar to athermal training). A distinct way to manipulate the high-field magnetization in exchange-biased systems, beyond the archetypical effects, was thus experimentally and theoretically demonstrated.

Enhanced 77 K vortex-pinning in Y Ba2Cu3O7−x films with Ba2Y TaO6 and mixed Ba2Y TaO6 + Ba2Y NbO6 nano-columnar inclusions with irreversibility field to 11 T

Pulsed laser deposited thin Y Ba2Cu3O7−x (YBCO) films with pinning additions of 5 at. % Ba2Y TaO6 (BYTO) were compared to films with 2.5 at. % Ba2Y TaO6 + 2.5 at. % Ba2Y NbO6 (BYNTO) additions. Excellent magnetic flux-pinning at 77 K was obtained with remarkably high irreversibility fields greater than 10 T (YBCO-BYTO) and 11 T (YBCO-BYNTO), representing the highest ever achieved values in YBCO films.

Vortex pinning at low temperature under high magnetic field in SmBa2Cu3Oy superconducting films with high number density and small size of BaHfO3 nano-rods

We have fabricated 5.6 vol.% BaHfO3 (BHO)-doped SmBa2Cu3Oy (SmBCO) films at a low substrate temperature of 750 °C by using the low temperature growth (LTG) technique with a seed layer. Using the LTG technique, we can obtain a purely c-axis oriented SmBCO film even at low growth temperatures. The LTG technique also greatly increases the number density of BHO nanorods. The size and matching field of the BHO nanorods in the films were 5.4 nm and 9.9 T. Transport measurements were carried out, and a high irreversibility field (Birr) and strong flux pinning force density (Fp) were obtained. The Birr was 15.1 T at 77 K for B//c. The maximum Fp of 407 GN m−3 in 10 T at 40 K and 770 GN m−3 from 9 to 17 T at 20 K have been measured. We believe that the LTG technique can be considered as important for improving of flux pinning performance in BaMO3 (BMO: M = Zr, Sn and Hf)-doped SmBCO coated conductors.

Broad temperature range study of Jc and Hirr anisotropy in YBa2Cu3Ox thin films containing either Y2O3 nanoparticles or stacking faults

Industrially optimized coated conductors generate very high current densities Jc and irreversibility field Hirr by quasi-empirical additions of multiple pin types. However, their microstructural complexity makes it hard to securely explain all aspects of their properties. We here describe the properties of two specially grown pulsed laser deposited YBa2Cu3Ox thin films with simpler pinning landscapes, for which we conducted detailed Jc(T, H, θ) and Hirr(T, H, θ) characterizations from 10 K to Tc, and in magnetic fields up to 31 T. One film has a random insulating Y2O3 nanoparticle distribution, while the second was grown with many ab-plane stacking faults. As a whole, the Y2O3-containing sample shows significantly higher Jc(θ) at all temperatures, except around the ab-plane at greater than 40 K. Consistent with our earlier studies of the effect of BaZrO3 (BZO) nanorods in commercial coated conductors, we find that there is significant additional Jc at low temperatures when insulating precipitates with strain mismatch are present that we attribute to point defect pinning that can resist thermal fluctuations only below about 30 K. In addition to this significantly enhanced low temperature Jc, the Y2O3-containing thin film also exhibits significantly reduced effective Ginzburg-Landau (G-L) anisotropy parameter fits for Hirr(θ), which fall to γeff ≈ 3.6 from the more usual γeff ≈ 5 in the stacking-fault containing thin film. Of significant practical importance is our finding that the Y2O3 containing film achieved a bulk flux pinning force density Fp of 1000 GN/m3 at 16 T and 4.2 K, a value about 30% larger than the mixed BZO-RE2O3 pin coated conductors which are presently the state of the art.

High-performance irreversibility field and flux pinning force density in BaHfO3-doped GdBa2Cu3Oy tape prepared by pulsed laser deposition

The high irreversibility field Bi and strong flux pinning force were obtained for BaHfO3-doped GdBa2Cu3Oy tapes on a metallic Hastelloy substrate with an ion beam-assisted deposition MgO buffer layer. At 77.3 K, Bi of 15.8 T and the maximum flux pinning force density of 23.5 GN/m3 for B ∥ c were achieved for the 1.5 vol % BaHfO3-doped GdBa2Cu3Oy tape, which are the world's highest recorded values for REBa2Cu3Oy-coated conductors on metallic substrates (RE = rare earth). From the flux pinning analysis, the c-axis correlated pinning by well-aligned BaHfO3 nanorods plays an important role in achieving the high irreversibility field and flux pinning force density performance.

Progress in Production and Performance of Second Generation (2G) HTS Wire for Practical Applications

Rare earth (RE) based second generation (2G) high temperature superconducting (HTS) wire is an emerging material that has been commercially available to a wide range of energy, scientific, industrial and medical applications including high-field magnets, fault current limiters, motors and generators, transformers, and power cables. High engineering critical current density, high mechanical strength, and high irreversibility field are the major advantages of 2G HTS wires over low temperature superconducting (LTS) wires and bismuth-based first generation (1G) HTS wires. 2G HTS wires with critical current I c (77K, self-field) of 300 ~ 500 A/cm-w and piece lengths of a few hundred meters are being routinely produced. Past and ongoing demonstration projects using the 2G HTS wires suggest that the practical application of this new material is appealing, promising and challenging. Further improvement in wire performance is desired and wire price is to be reduced. In this paper, important properties of 2G wires such as uniformity, in-field Ic and electromechanical behaviors are described. Recent technology advancements in using 2G HTS wire for practical applications are discussed.

Strong enhancement of high-field critical current properties and irreversibility field of MgB2 superconducting wires by coronene active carbon source addition via the new B powder carbon-coating method

We report an effective carbon-containing additive, coronene (C24H12), for MgB2 superconducting wires. We used B powder coated with C24H12 to fabricate MgB2 wires using the powder-in-tube (PIT) and internal Mg diffusion (IMD) processes. The in-field critical current properties are strongly enhanced for both PIT- and IMD-processed MgB2 wires. For PIT MgB2 wires, a critical current density (Jc) value of 1.8 × 104 A cm−2 is obtained at 4.2 K and 10 T. For IMD MgB2 wires, we obtained a Jc of 1.07 × 105 A cm−2 and an engineering Jc (Je) of 1.12 × 104 A cm−2 at 4.2 K and 10 T. These Jc and Je values are similar to the highest values reported for MgB2 wires thus far. Furthermore, the irreversibility field, Birr, determined with a current density criterion of 100 A cm−2, is strongly enhanced to 25 T at 4.2 K, which is also the highest value reported for MgB2 superconducting wires thus far. Coronene is an active carbon source for MgB2 superconducting wires because (1) coronene has a high carbon content (96 wt%) with a small amount of hydrogen (impurity), (2) the decomposition temperature for coronene is near the reaction temperature between Mg and B, and (3) uniform dispersion of coronene on the B surface can be obtained due to the melting point of coronene being lower than the decomposition temperature. Carbon substitution for B caused by the coronene active carbon source is mainly responsible for the high field critical current properties and the high Birr obtained in this work.

The Effects of Ti Addition and High Cu/Sn Ratio on Tube Type <formula formulatype="inline"> <tex Notation="TeX">$(\hbox{Nb}, \hbox{Ta})_{3}\hbox{Sn}$</tex></formula> Strands, and a New Type of Strand Designed to Reduce Unreacted Nb Ratio

In this paper, we report the properties of two tube type Ta doped Nb3Sn strands: one strand was additionally Ti doped by way of a Sn-Ti alloy core, and the other had high Cu/Sn ratio within the filaments. Higher irreversibility field (Birr) was obtained on the quaternary strand with respect to the (Nb-7.5 wt.%Ta)3Sn strand. High Cu/Sn ratio decreased the amount of coarse grain formation, but also degraded the layer Jc of the tube type strand by depressing the Sn content in the fine grain (FG) layer. A new type of strand, the subelement of which is composed of seven bare Cu-Sn cored Nb tube filaments, was designed with the aim to reduce the unreacted Nb area fractions. The test results of the first experimental strand are reported. The unreacted Nb ratio is reduced relative to normal tube type strands and the FG area fraction is improved. The unique structure of this strand makes it also possible to improve the stoichiometry of FG and reduce the effective diameter (deff) .

Strongly enhanced vortex pinning from 4 to 77 K in magnetic fields up to 31 T in 15 mol.% Zr-added (Gd, Y)-Ba-Cu-O superconducting tapes

Applications of REBCO coated conductors are now being developed for a very wide range of temperatures and magnetic fields and it is not yet clear whether vortex pinning strategies aimed for high temperature, low field operation are equally valid at lower temperatures and higher fields. A detailed characterization of the superconducting properties of a 15 mol. % Zr-added REBCO thin film made by metal organic chemical vapor deposition, from 4.2 to 77 K under magnetic fields up to 31 T is presented in this article. Even at a such high level of Zr addition, Tc depression has been avoided (Tc = 91 K), while at the same time an exceptionally high irreversibility field Hirr ≈ 14.8 T at 77 K and a remarkably high vortex pinning force density Fp ≈ 1.7 TN/m3 at 4.2 K have been achieved. We ascribe the excellent pinning performance at high temperatures to the high density (equivalent vortex matching field ∼7 T) of self-assembled BZO nanorods, while the low temperature pinning force is enhanced by large additional pinning which we ascribe to strain-induced point defects induced in the REBCO matrix by the BZO nanorods. Our results suggest even more room for further performance enhancement of commercial REBCO coated conductors and point the way to REBCO coil applications at liquid nitrogen temperatures since the critical current density Jc(H//c) characteristic at 77 K are now almost identical to those of fully optimized Nb-Ti at 4 K.

Sol–gel auto-combustion synthesis of PVP/CoFe2O4 nanocomposite and its magnetic characterization

Poly(vinyl pyrrolidone)/CoFe2O4 nanocomposite has been fabricated by a sol–gel auto-combustion method. Poly(vinyl pyrrolidone) was used as a reducing agent as well as a surface capping agent to prevent particle aggregation and stabilize the particles. The average crystallite size estimated from X-ray line profile fitting was found to be 20±7nm. The high field irreversibility and unsaturated magnetization behaviours indicate the presence of the core–shell structure in the sample. The exchange bias effect observed at 10K suggests the existence of the magnetically aligned core surrounded by spin-disordered surface layer. The reduced remanent magnetization value of 0.6 at 10K (higher than the theoretical value of 0.5) shows the PVP/CoFe2O4 nanocomposite to have cubic magnetocrystalline anisotropy according to the Stoner–Wohlfarth model.