Critical current density, lower critical field, and flux creep in Ag-sheathed high-J c tape of Bi-Pb-Sr-Ca-Cu-O

Abstract

Initial magnetization curve M(H) and magnetic relaxation M(t) were studied on the Ag-sheathed and highly c-axis oriented tape of Bi-Pb-Sr-Ca-Cu-O with transport Jct=5400 and 2400 A/cm2 (77 K, H=0). The Jc value, derived from M(H) curve based on Bean’s critical-state model, agrees fairly well with the Jct. The lower critical field Hc1 for H⊥c axis from M(H) curve increases with a slope of −0.2 Oe/K as temperature decreases from Tc, and it approaches the saturated value of 15 Oe at T∼0 K. The magnitude is much lower than that for the high-Tc superconductors La-Sr-Cu-O and Y-Ba-Cu-O. The creep rate and activation energy U0 are evaluated from M(t) based on the flux creep model. The results show a significant dependence on the measuring process and magnetic field H. The U0 at 5 K for H=500 Oe (H⊥c) is 0.4 eV for the in-field magnetization (IN) and 0.1 eV for the remanent magnetization (REM), which are larger than those for Bi-based high-Tc superconductors reported previously. The U0 for the IN shows a peak of 0.8 eV around 30 K and then decreases as temperature increases, while a peak in it is weakened for the REM. The U0 at H=30 Oe (H⊥c) for the IN is one order larger than that for 500 Oe and the peak temperature is shifted to the lower temperature (∼10 K).

Superconductors and Lenz’s law

“…The maximum surface magnetic flux density is about 350 mT for this NdFeB magnet. We are certain that at the very beginning of the interaction the strength of the magnetic field around the superconducting coil is smaller than the lower critical field H c1 of HTS materials-which is anisotropic and no greater than a few tens of mT at 77 K [19][20][21][22][23][24]. Thus, the superconducting coil is in the Meissner state and there is no magnetic flux in the region inside the coil.…”

Finite voltages along the c-direction of Bi-2223/Ag multifilament tape

“…Ag-sheathed Bi-based superconducting tapes are the most promising family of high-T c superconductors for high critical current and long length applications. Much effort has been made to increase the critical current density and mechanical properties of the tapes [1][2][3][4]. The success in the fabrication of Bi-based Ag-sheathed multifilament tapes is significant progress towards this goal.…”

The critical current anisotropy of the Ag-(Bi Pb)2Sr2Ca2Cu3Oxtape form conductor

“…The investigation of the critical current (Ic) anisotropy of textured, layered superconducting Ag-"2223" tape-form conductors, (with critical current density 104 Acm-2 [I]), is of physical and technological importance. Currently, magnetic flux creep in these conductors limits their high magnetic field application at liquid nitrogen temperatures [2]; this is caused by imperfect connections between Cu02 planes through the grain boundaries in pollycrystalline tapes rather than the intrinsic properties of the "2223" phase itself 13.1. In this paper, the influence of the angular magnetic field rotation, and the r p !…”