Current-voltage characteristics and flux creep in melt-textured YBa2Cu3O7−δ

Abstract. We investigated the current–voltage (E–J) characteristics in melt-textured YBa2Cu3O7− strips by measuring the magnetic-field sweep rate dependence of magnetization. We took account of the current density J distribution in the specimen using a previously developed method (Mawatari Y et al 1997 Appl. Phys. Lett. 70 2300). For a wide temperature and magnetic-field range (60–80 K, 0.2–5.0 T), the E–J curves in the electric-field window E D 10−10–10−5 V m−1 exhibited power-law behaviour E / J n, and the power index n generally became smaller at higher magnetic fields and temperatures. In low magnetic fields (0Ha 6 0:5 T) the n values were large (>20), and thus the Bean model becomes a good approximation. The E–J characteristics in the lower E window were also derived from the relaxation of magnetization, the flux creep, and we found that the wide-range E–J characteristics exhibit near-power-law behaviour but that there exist slight downward curvatures in the log E versus log J plots. This downward curvature reveals that the dissipation approaches zero when the current is substantially reduced. The drastic decrease of the flux creep, which was observed when the sample temperature was decreased in a fixed magnetic field, is consistent with the observed E–J characteristics. 1