Recent advances in iron-based superconductors toward applications

Abstract

Iron with a large magnetic moment was widely believed to be harmful to the emergence of superconductivity because of the competition between the static ordering of electron spins and the dynamic formation of electron pairs (Cooper pairs). Thus, the discovery of a high critical temperature (Tc) iron-based superconductor (IBSC) in 2008 was accepted with surprise in the condensed matter community and rekindled extensive study globally. IBSCs have since grown to become a new class of high-Tc superconductors next to the high-Tc cuprates discovered in 1986. The rapid research progress in the science and technology of IBSCs over the past decade has resulted in the accumulation of a vast amount of knowledge on IBSC materials, mechanisms, properties, and applications with the publication of more than several tens of thousands of papers. This article reviews recent progress in the technical applications (bulk magnets, thin films, and wires) of IBSCs in addition to their fundamental material characteristics. Highlights of their applications include high-field bulk magnets workable at 15-25 K, thin films with high critical current density (Jc) > 1 MA/cm2 at ~10 T and 4 K, and an average Jc of 1.3*104 A/cm2 at 10 T and 4 K achieved for a 100-m-class-length wire. These achievements are based on the intrinsically advantageous properties of IBSCs such as the higher crystallographic symmetry of the superconducting phase, higher critical magnetic field, and larger critical grain boundary angle to maintain high Jc. These properties also make IBSCs promising for applications using high magnetic fields.Comment: Published online in Materials Today. Open Acces

Unique defect structure and advantageous vortex pinning properties in superconducting CaKFe4As4

“…Similarly, various techniques have been exploited to introduce artificial defects in iron-based superconductors (IBSs) since their discovery. 13,14 As in the case of YBCO, Jc has been enhanced particularly for AEFe2As2-based (AE: alkaline-earth element) superconductors, the so-called 122 materials, by particle irradiation, 15 addition of BaZrO3, 16,17 fabrication of superlattices, 18 and introduction of stacking faults. 19,20 By devising the fabrication process, a significant progress has been achieved in improving Jc of bulks and thin films so far, while further Jc enhancement is required towards real-life applications.…”

Synthesis of electron- and hole-doped bulk BaFe2As2 superconductors by mechanical alloying

“…The SC state also can be obtained by isovalent atomic substitution of As 3+ for P 3+ and Fe 4+ for Ru 4+ [22]. The upper critical field in Ba − 122 superconducting compounds is estimated to be more than 60T, with a critical current of up to 10 6 A/cm 2 [17,23,24]. Thus, such superconductors are applicable for highfield and high-current application such as superconducting wires, magnets, fault current limiters etc.…”

Strong pinning in the hole-doped pnictide superconductor La0.34Na0.66Fe2As2

“…Vortex dynamics and pinning mechanism in IBS is quite interesting due to its salient features [12][13][14][15] such as, low Ginzburg number (G i ) [16], small anisotropy [17], high intergrain connectivity [18], high upper critical field [19] and moderate T c [20]. These properties are vital for technological applications of type-II superconductors [3,4]. In-spite of low Ginzburg number (G i ) the vortex phase-diagram of IBS and low-T c superconductors (LTS) are quite different in the sense that the upper critical-field, H c2 (T), and the irreversibility line, H irr (T), are separated by a broad vortex-liquid region in IBS [21], whereas, in LTS, no appreciable vortex-liquid region exist.…”

“…The effect of particle irradiation on the vortex dynamics and J c would be interesting to explore in the present sample. A detailed review of the critical current density and pinning in bulk, thin films, tapes and wires of IBS for technological importance is provided in Refs [3,4]…”