Study Of Current Dependent Activation Energy U(J) On High J(C) Melt-Textured Yba2cu3o7

Magnetic relaxation of melt-textured YBa2Cu3O7 with high J(c) was measured in order to investigate the current dependence of effective activation energy U(J). The activation energy value U(J) on a narrow range of J was calculated directly from the relaxation curves, while the U(J) function on a wide range of J value was obtained both by temperature field modifications of U(J). The two gained U(J) functions are exactly the same: V(J)=U-o [(J(c)/J)(mu) -1]/mu, which means the pinning mechanism of our sample is collective pinning.