Transport critical current density of (Bi_1.6Pb_0.4)Sr₂Ca₂Cu₃O₁₀/Ag superconductor tapes with addition of nanosized CoFe₂O₄

Abstract

The effect of nanosized CoFe₂O₄ (60 nm) addition on the transport critical current density, J _c, of (Bi_1.6Pb_0.4)Sr₂Ca₂Cu₃O₁₀(CoFe₂O₄) _x (x = 0–0.05 wt%) superconductor prepared by the co-precipitation method was investigated. The optimal J _c (measured using the four-point probe method) was observed in the x = 0.01 wt% pellets. Using this optimal wt%, Ag-sheathed (Bi_1.6Pb_0.4)Sr₂Ca₂Cu3O₁₀(CoFe₂O₄)_0.01 superconductor tapes were fabricated using the powder-in-tube method. The tapes were sintered for 50 and 100 h at 845 °C. The phase and microstructure of the samples were determined using the powder X-ray diffraction method and scanning electron microscopy, respectively. The temperature dependence of J _c for the tapes in various applied magnetic fields was also measured. J _c of (Bi_1.6Pb_0.4)Sr₂Ca₂Cu₃O₁₀(CoFe₂O₄)_0.01/Ag tapes sintered for 100 h was 22,420 A/cm² at 30 K. The non-added tapes sintered for 100 h showed a much lower J _c (8280 A/cm² at 30 K). This study showed that addition of CoFe₂O₄ nanoparticles enhanced the transport critical current density in the (Bi_1.6Pb_0.4)Sr₂Ca₂Cu₃O₁₀ superconductor tapes. This result is consistent with the previous calculations on frozen flux superconductor in a nanomagnet–superconductor hybrid system.