Time decay of the magnetic properties of type-II superconductors in the presence of large pinning centers

We present a study of the time decay of magnetic states in type-II superconductors. The mean escape time of flux quanta from the pinning centers is calculated by considering the well-known washboard potential and a pinning potential appropriate to the case of pinning center dimensions l much larger than the coherence length xi. We find that, in both cases, the attempt frequency in the Arrhenius formula depends on the current density J. Finally, by plotting the E(J) curves, we show that the dissipation due to flux creep mechanisms goes to zero much faster in the second case, where l much greater than xi is assumed. (C) 1997 Elsevier Science B.V.