Study of magnetization relaxation on zone-melted YBa(2)Cu(3)O(6+x) superconductors

SQUID studies of magnetic relaxation and hysteresis on a zone-melted YBa2Cu3O(6+x) sample suggest a nonlogarithmic magnetization decay at high temperature, which can be attributed to a nonlinear U(J) relationship originating from the local pinning potential Up(x). The U(J) relationship helps determine the local pinning potential to be Up(x) = U0(x/x0)(1-ln(x/x0)).