Transport critical current density of (Bi_(1.6)Pb_(0.4))Sr_2Ca_2Cu_3O_(10)/Ag superconductor tapes with addition of nanosized CoFe_2O_4

摘要

The effect of nanosized CoFe_2O_4 (60 nm) addition on the transport critical current density, Jc, of (Bi_(1.6)Pb_(0.4))Sr_2Ca_2Cu_3O_(10)/(CoFe_2O_4)_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_(1.6)Pb_(0.4))-Sr_2Ca_2Cu_3O_(10)(CoFe_2O_4)_(0.01) superconductor tapes were fabricated using the powder-in-tube method. The tapes were sintered for 50 and 100 h at 845 ℃. 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 Jc for the tapes in various applied magnetic fields was also measured. Jc of (Bi_(1.6)Pb_(0.4))Sr_2Ca_2Cu_3O_(10)(CoFe_2O_4)_(0.01)/Ag tapes sintered for 100 h was 22,420 A/cm~2 at 30 K. The non-added tapes sintered for 100 h showed a much lower J_c (8280 A/cm~2 at 30 K). This study showed that addition of CoFe_2O_4 nanoparticles enhanced the transport critical current density in the (Bi_(1.6)Pb_(0.4))Sr_2Ca_2Cu_3O_(10) superconductor tapes. This result is consistent with the previous calculations on frozen flux superconductor in a nanomag-net-superconductor hybrid system.