Trapped field potential of commercial Y-Ba-Cu-O bulk superconductors designed for applications

Bulk high-temperature superconductors (HTSs) that act as a trap field magnet establish a novel type of magnetic field source, which is significantly different from that of a permanent magnet or solenoid; therefore, they can be potentially used in magnetic-force-based applications. However, the primary issues related to the commercial use of the bulk HTS technology are established on the enhancement of trapped magnetic fields, as well as their reliability and reproducibility at temperatures achievable with off-the-shelf cryocoolers. This study presents experimental investigations on the strong trapped magnetic fields observed in commercial Y-Ba-Cu-O bulk HTSs produced as a double-sample stack, a cylindrical bulk, and a ring-shaped bulk. Consequently, a reliable and reproducible magnetic field of 9.5 T at 50 K was trapped in commercial Y-Ba-Cu-O assembled as a double-sample stack. In this case, shrink-fit encapsulation with either aluminum or stainless steel tube ensured equally effective reinforcement. Higher magnetization, although accompanied with partial flux jumps, yielded a trapped field of 16.85 T at 30 K, which is comparable to the reported record trapped fields. Finally, a maximum trapped field of 9.78 T - the strongest trapped field reported to date - was attained in the 6 mm hollow space of the ring-shaped bulk HTS

35.4 T field generated using a layer-wound superconducting coil made of (RE)Ba2Cu3O7-x (RE = Rare Earth) coated conductor

To explore the limits of layer wound (RE)Ba2Cu3O7-x (REBCO, RE = Rare Earth) coils in a high magnetic field environment > 30 T, a series of small insert coils have been built and characterized in background fields. One of the coils repeatedly reached 35.4 T using a single ~100 m length of REBCO tape wet wound with epoxy and nested in a 31 T background magnet. The coil was quenched safely several times without degradation. Contributing to the success of this coil was the introduction of a thin polyester film that surrounded the conductor. This approach introduces a weak circumferential plane in the coil pack that prevents conductor delamination that has caused degradation of several epoxy impregnated coils previously made by this and other groups.Comment: 7 pages, 3 figures, 1 tabl

A Trapped Field of 17.6 T in Melt-Processed, Bulk Gd-Ba-Cu-O Reinforced with Shrink-Fit Steel

The ability of large grain, REBa$_{2}$Cu$_{3}$O$_{7-\delta}$ [(RE)BCO; RE = rare earth] bulk superconductors to trap magnetic field is determined by their critical current. With high trapped fields, however, bulk samples are subject to a relatively large Lorentz force, and their performance is limited primarily by their tensile strength. Consequently, sample reinforcement is the key to performance improvement in these technologically important materials. In this work, we report a trapped field of 17.6 T, the largest reported to date, in a stack of two, silver-doped GdBCO superconducting bulk samples, each of diameter 25 mm, fabricated by top-seeded melt growth (TSMG) and reinforced with shrink-fit stainless steel. This sample preparation technique has the advantage of being relatively straightforward and inexpensive to implement and offers the prospect of easy access to portable, high magnetic fields without any requirement for a sustaining current source.Comment: Updated submission to reflect licence change to CC-BY. This is the "author accepted manuscript" and is identical in content to the published versio

High-field transport properties of a P-doped BaFe₂As₂ film on technical substrate

High temperature (high-Tc) superconductors like cuprates have superior critical current properties in magnetic fields over other superconductors. However, superconducting wires for high-field-magnet applications are still dominated by low-Tc Nb3Sn due probably to cost and processing issues. The recent discovery of a second class of high-Tc materials, Fe-based superconductors, may provide another option for high-field-magnet wires. In particular, AEFe2As2 (AE: Alkali earth elements, AE-122) is one of the best candidates for high-field-magnet applications because of its high upper critical field, Hc2, moderate Hc2 anisotropy, and intermediate Tc. Here we report on in-field transport properties of P-doped BaFe2As2 (Ba-122) thin films grown on technical substrates by pulsed laser deposition. The P-doped Ba-122 coated conductor exceeds a transport Jc of 105 A/cm2 at 15 T for main crystallographic directions of the applied field, which is favourable for practical applications. Our P-doped Ba-122 coated conductors show a superior in-field Jc over MgB2 and NbTi, and a comparable level to Nb3Sn above 20 T. By analysing the E − J curves for determining Jc, a non-Ohmic linear differential signature is observed at low field due to flux flow along the grain boundaries. However, grain boundaries work as flux pinning centres as demonstrated by the pinning force analysis

Time reversal invariant single gap superconductivity with upper critical field larger than Pauli limit in NbIr2_2B2_2

Recently, compounds with noncentrosymmetric crystal structure have attracted much attention for providing a rich playground in search for unconventional superconductivity. NbIr$_2$B$_2$ is a new member to this class of materials harboring superconductivity below $T_{\rm c} = 7.3(2)$~K and very high upper critical field that exceeds Pauli limit. Here we report on muon spin rotation ($\mu$SR) experiments probing the temperature and field dependence of effective magnetic penetration depth in this compound. Our transverse-field -$\mu$SR results suggest a fully gaped $s$-wave superconductvity. Further, the estimated high value of upper critical field is also supplemented by high field transport measurements. Remarkably, the ratio $T_{\rm c}$/$\lambda^{-2}(0)$ obtained for NbIr$_2$B$_2$ ($\sim$2) is comparable to those of unconventional superconductors. Zero-field $\mu$SR data reveals no significant change in the muon spin relaxation rate above and below $T_{\rm c}$, evincing that time-reversal symmetry is preserved in the superconducting state. The presented results will stimulate theoretical investigations to obtain a microscopic understanding of the origin of superconductivity with preserved time reversal symmetry in this unique noncentrosymmetric system.Comment: 8 pages, 4 figures. arXiv admin note: text overlap with arXiv:2101.0823

High field superconducting properties of Ba(Fe1-xCox)2As2 thin films

The film investigated grew phase-pure and highly textured with in-plane and out-of-plane full width at half maximum, FWHM, of = 0.74° and = 0.9°, Suppl. S1. The sample, however, does contain a large density of ab-planar defects, as revealed by transition electron microscope (TEM) images of focused ion beam (FIB) cuts near the microbridges, Fig. 1. These defects are presumably stacking faults (i.e. missing FeAs layers)20. The reason for this defect formation (also observed on technical substrates)21 is not fully understood. Possible reasons are a partial As loss during deposition22, and relaxation processes in combination with the Fe buffer layer23. Estimating the distance between these intergrowths leads to values varying between 5 and 10 nm. Between the planar defects, an orientation contrast is visible in TEM (inset Fig. 1b), i.e. the brighter crystallites are slightly rotated either around (010) (out-of-plane spread, ) or around (001) (in-plane spread, ) and enclosed by dislocation networks or small-angle GBs. Since the crystallites are sandwiched between planar defects, an in-plane misorientation is most likely. The out-of-plane misorientation, on the other hand, is visible as a slight tilt of the ab-planar defects with respect to each other, especially in the upper part of the sample. No globular or columnar precipitates were found