Critical Current Density of Wire Type Y-Ba-Cu Oxide Superconductor

Abstract

We have fabricated wire type Y-Ba-Cu oxide superconductor by powder metallurgy technique. A large critical current density J _c of 7.25 × 10² A/cm² at 77 K and 0 T and the resistive T _c transition of 89 K to 87 K were obtained for the wire type conductor heat treated without Cu sheath. However, the J _c(77 K) drastically decreased by a factor of 200, applying a magnetic field of 1 T. On the contrary, J _c(4.2 K) little changed; 1.63 × 10² A/cm² at 1 T and 1.33 × 10² A/cm² at 12 T. Based on the magnetic field dependence of J _c, we estimate upper critical field Bc₂ (i.e. corresponding to Bc₂ defined by T _c (offset)) and GL coherence length ζ.