Magnetic Nanoparticles as Pinning Center in Bi-Sr-Ca-Cu-O/Ag Superconductor Tapes

This paper reports on the effectiveness of magnetic nanoparticles as pinning center in the Bi-based superconductor tapes. Nanosize γ-Fe2O3 and ultrafine Fe3O4 have been employed to enhance the transport current density of Ag-sheathed-(Bi1.6Pb0.4)Sr2Ca2Cu3O10 superconductor tapes prepared by the powder-in-tube technique. The transport critical current density, Jc of (Bi1.6Pb0.4)Sr2Ca2Cu3O10-(γ-Fe2O3)0.01, sintered at the optimum temperature of 845 oC is 6490 A/cm2 when measured at 77 K. A further single intermediate rolling step increases Jc to 9560 A/cm2. Samples without γ-Fe2O3 prepared under the same condition showed a lower Jc with a maximum of 1560 A/cm2. Similar results are also obtained for ultrafine Fe3O4. Magnetic impurities generally suppress superconductivity. However, our study shows great promise of magnetic nanorod γ-Fe2O3 and ultrafine Fe3O4 as novel pinning centers in enhancing the transport critical density of Ag sheathed Bi-Sr-Ca-Cu-O superconductor tapes. This is in line with previous calculations on frozen flux superconductor with magnetic nanoparticle as pinning centers.