Search

Since the report by Fietz and Webb (Phys. Rev.1968, 178, 657–667), who considered the pinning force density, F p → = J c → × B → (where Jc is the critical current density and B is applied magnetic flux density), in isotropic superconductors as a unique function of reduced magnetic field, B B c 2 (where B c 2 is the upper critical field), F p → has been scaled based on the B B c 2 ratio, for which there is a widely used Kramer–Dew–Hughes scaling law of F p → B = F p , m a x B B c 2 p 1 − B B c 2 q , where F p , m a x , B c 2 , p, and q are free-fitting parameters. To describe F p → B in high-temperature superconductors, the Kramer–Dew–Hughes scaling law has been modified by (a) an assumption of the angular dependence of all parameters and (b) by the replacement of the upper critical field, Bc2, by the irreversibility field, Birr. Here, we note that F p → is also a function of critical current density, and thus, the F p → J c scaling law should exist. In an attempt to reveal this law, we considered the full F p → B , J c function and reported that there are three distinctive characteristic ranges of B B c 2 , J c J c s f (where J c s f is the self-field critical current density) on which F p → B , J c can be splatted. Several new scaling laws for F p → J c were proposed and applied to MgB2, NdFeAs(O,F), REBCO, (La,Y)H10, and YH6. The proposed scaling laws describe the in-field performance of superconductors at low and moderate magnetic fields, and thus, the primary niche for these laws is superconducting wires and tapes for cables, fault current limiters, and transformers. [ABSTRACT FROM AUTHOR]

Magnesium diboride (MgB2) thin films on r-cut sapphire (r-Al2O3) single crystals were fabricated by a precursor, which was obtained at room temperature via a pulsed laser deposition (PLD) method using a Nd:YAG laser, and an in situ postannealing process. The onset superconducting transition, Tconset, and zero-resistivity transition, Tczero, were observed at 33.6 and 31.7 K, respectively, in the MgB2 thin films prepared by a Mg-rich target with a ratio of Mg:B = 3:2. The critical current density, Jc, calculated from magnetization measurements reached up to 0.9 × 106 A cm−2 at 20 K and 0 T. The broad angular Jc peak was found at 28 K when the magnetic fields were applied in a direction parallel to the film surface (θ = 90°). This could be indicative of the granular structure with randomly oriented grains. Our results demonstrate that this process is a promising candidate for the fabrication of MgB2 superconducting devices. [ABSTRACT FROM AUTHOR]