Pinning-force density of superconducting Bi-2223 tape wires

The pinning-force density and the irreversibility field are measured for Bi-2223 tape wires at various temperatures under the magnetic fields normal and parallel to the c-axis. It is found that the scaling laws of pinning-force density in the low- and high-temperature regions and the temperature dependence of the irreversibility field are formally the same between the two field directions in spite of some anisotropy factor, suggesting that the pinning mechanism is essentially the same for the two field directions. These results are compared with the numerical calculation based on the flux-creep model. The experimental results are well explained by the theory including the anisotropic property.

The pinning potential estimated from the flux-creep theory at 80 K and 1.0 T is of the order of several 10 meV and the factor of the anisotropy is about 1.3. The value of the pinning potential under the magnetic field along the c-axis suggests that the flux lines are strongly connected along this direction. The longitudinal elastic correlation length of the flux lines is of the order of several μm and this supports the hypothesis.

The pinning characteristics of a Bi-2223 tape wire to which the strong pinning centers are successfully introduced are discussed using the flux-creep theory for evaluating the potential of this material for application. The irreversibility field for the direction parallel to the c-axis is estimated to be sufficiently high even at 77.3 K and it is concluded that Bi-2223 has a sufficient potential for application.