Transport Critical Current Density of Bi-Sr-Ca-Cu-O/Ag Superconductor Tapes with Addition of Fe_3O_4 as Flux Pinning Center

摘要

This paper reports on the flux pinning capability of micron size Fe_3O_4 in Bi-Sr-Ca-Cu-O superconductor tapes. Ag sheathed high temperature superconductor tapes with starting compositions (Bi,Pb)_2Sr_2Ca_2Cu_3O_(10) (2223) and (Bi,Pb)_2Sr_2Ca_2Cu_3O_(10)(Fe_3O_4)_(0.01) were fabricated using the powder in tube method. The Bi-Sr-Ca-Cu-O powders were prepared by using the co-precipitation technique. The effects of Fe_3O_4 addition on the microstructure, phase formation, critical temperature and transport critical current density, J_c were studied. The J_c value of the Fe_3O_4 added tapes is higher (6,090 A/cm~2 at 77 K and 24,500 A/cm~2 at 30 K, in zero field) than the non-added tapes (3,730 A/cm~2 at 77 K and 13,3180 A/cm~2 at 30 K, in zero field). A sudden decrease of J_c in low magnetic fields(B < 0.12 T) when applied parallel (B_‖) and perpendicular (B_⊥) to the tapes surface was observed. The destruction of weak links played an important role in the early J_c suppression. The rate of decrease of J_c was observed to decrease when the magnetic field was increased further. Improvement in the flux pinning was observed in (Bi, Pb)_2Sr_2Ca_2Cu_3O_(10)-(Fe_3O_4)_(0.01) tapes. This study shows that magnetic particles such as Fe_3O_4 can act as effective pinning centers leading to the enhancement of J_c in the system.