Pinning characteristics of (Nb,Ta)/sub 3/Sn superconductors produced by Nb/Ta-Sn composite process

Pinning properties in (Nb,Ta)/sub 3/Sn superconductors produced by a Nb/Ta-Sn composite process are studied through the measurement of the temperature and magnetic field dependences of J/sub c/ and its anisotropy with respect to the field direction, referring to the grain morphology and the compositional analysis of the (Nb,Ta)/sub 3/Sn phase. The experimental result of the anisotropy in J/sub c/ and the observation of the grain morphology suggest that the contribution of the grain boundary to the pinning force density is not large. Two regions having different grain morphologies can be seen in the (Nb,Ta)/sub 3/Sn layer, where the boundary of the two regions roughly corresponds to the boundary between the Nb-Ta sheath and the Ta-Sn core in the initial Nb-Ta/Ta-Sn mono-core composite before reaction. Such a boundary between the two regions inside the (Nb,Ta)/sub 3/Sn phase and/or a S-N interface of the boundary between the Nb-sheath and the (Nb,Ta)/sub 3/Sn superconducting phase would influence the pinning property. Both are possible reasons for the anisotropy in J/sub c/. On the other hand, the so-called "peak effect" is recognized in the flux pinning, suggesting that another pinning mechanism acts in high field, differing from that in low field.