Transport Critical Current Density of Ag-Sheathed Bi-Sr-Ca-Cu-O Multifilament Superconductor Tapes with Magnetic Nanopowders γ-Fe₂O₃

The transport critical current density of multifilament Ag/Bi-Sr-Ca-Cu-O tapes with the addition of magnetic nanopowder (γ-Fe₂O₃) has been measured. The tapes were prepared using the powder in tube method with 30 filaments. Three types of Bi-Sr-Ca-Cu-O starting materials namely from solid state reaction without γ-Fe₂O₃, solid state reaction with γ-Fe₂O₃ addition and ultrafine powders prepared by coprecipitation method with γ-Fe₂O₃ have been used. The starting composition of the γ-Fe₂O₃ added samples is Bi_1.6Pb_0.4Sr₂Ca₂Cu₃O₁₀-(γ-Fe₂O₃)_0.01. The first intermediate rolling enhances J_c but subsequent rolling shows no improvement in J_c. Tapes prepared from coprecipitation powders with γ-Fe₂O₃ added showed the highest J_c of 7890 A/cm² at 77 K and in self-field after the first intermediate rolling. These results suggest that intermediate rolling and magnetic nanopowders can be used to improve the critical current density of multifilament Ag/Bi-Sr-Ca-Cu-O superconductor tapes.