Macroscopic Magnetic Properties of High Temperature Superconductors

Superconducting materials for large scale applications

“…, at which the bulk vanishes [19]. Under equilibrium conditions magnetic flux penetrates the bulk of a Type II superconductor above a lower critical field , which is 100 mT for the materials under consideration [19].…”

“…Under equilibrium conditions magnetic flux penetrates the bulk of a Type II superconductor above a lower critical field , which is 100 mT for the materials under consideration [19]. This magnetic flux exists as an array of flux-quantized line vortices or fluxons, which can be spatially ordered or disordered, static or liquid-like.…”

“…At absolute zero, superconducting current can flow without any loss (i.e., at zero voltage) up to a critical current , corresponding to the maximum pinning strength. However, at finite temperature, thermal activation can cause "flux creep" of vortices down the macroscopic fluxon density gradient (actually a small amount of creep can occur even at absolute zero because of quantum tunneling of vortices, observed in HTS materials) [19]- [21]. In most materials with random microstructural defects, the vortex structure is disordered or glassy in nature, and vortex glass theory predicts that flux creep gives rise to a voltage-current relationship, where is called the "index value" [20], [21].…”

“…, which is a function of temperature and which is much lower than for HTS materials, major changes occur in the vortex structure [19]. These changes have been described by a variety of theories-for example, the vortex glass melting theory, in which vortices above are in an unpinned, liquid-like state.…”

The Influence of Nano-SiC on the Flux Pinning of YBa2Cu3O7—y/Nano-SiC Composites

“…This limitation is intrinsic and arises from the well known characteristics of HTSC, such as, large anisotropy and short coherence lengths that lead to a weak pinning of flux lines [3 to 6]. Second, in polycrystalline HTSC materials, J c is confined by poor alignments of the grains and chemical heterogeneity, which lead to weak links with low values of critical current density J c [3,7]. The week link problem is greatly overcome by various texture-growth methods, such as the powder-in-tube method with following thermal and mechanical treatments for fabricating Bi 2 Sr 2 Ca 2 Cu 3 O 10 /Ag superconducting tapes [3, 8 to 10].…”