As the pinning performance due to secondary phase particles is inversely proportional to the average particle size, a successful refinement of the secondary phase particles up to nanometer level resulted in a considerable increase of super-current density at 77 K. The samples exhibited not only the highest Jc ever reported for bulk melt-processed samples but also enabled for the first time levitation at liquid oxygen temperature (90.2 K). The new nanometer-scale pinning medium, with size in the range 20-50 nm, was composed of Zr-rich ball-milled Gd-211 particles. The super-current density reached 200 and 110 kA/cm2 at 0 and 3 Tesla, respectively, and 55 kA/cm2 at 90 K in the remnant state. We thus reached the internal ISTEC goal in electro-magnetic properties of materials intended for large-scale bulk applications. For details, see the paper by Muralidhar et al., Applied Physics Letters 83, 5005 (2003). These results were covered by Japanese patent No. KN02B317-2, Date of filling March 31, 2005.
Researchers develop an optimized recipe for retaining superconductivity in bulk MgB2 by enhancing its critical current density. Magnesium diboride (MgB2) superconductors show great promise for