Flux pinning and flux creep in melt-textured (Y1-xPrx)Ba2Cu3O7- delta

Abstract

Flux pinning and flux creep behaviour for the H//c axis have been investigated on a set of MTG (Y1-xPrx)Ba2Cu3O7- delta (x<or=0.08) samples. The critical current densities Jc, apparent pinning potential U0* and effective activation energy Ueff(J,T) have been derived from the corresponding magnetic hysteresis and relaxation measurements. The qualitative temperature and field dependences of the critical current densities are found to be unaffected by the Pr doping, up to the highest concentration level, in the present study. The temperature-dependent profiles of the normalized relaxation rate S show similar features, all including the initial linear and so-called plateau regions (roughly) with a peak interposed between them. Compared with the pure YBa2Cu3O7- delta , the Jc, U0*, J and Ueff(J,T) values get enhanced for all the Pr-doped samples, with an optimal effect achieved at Pr concentration around x=0.05. A scaling relation Ueff(J,T)=UiG(T)F(Ji/J) at a given magnetic field is used to analyse the Ueff(J,T) data, where Ui and Ji are the scales of activation energy and current density, respectively, and G(T) is either determined by a constructive scaling procedure or empirically chosen as G(T)=(1-(T/T1)2)3/2. The current-density-dependent behaviour of Ueff(J,T)/G(T), together with the observed S(T) feature and field-independent phenomenon of Jc(H), is qualitatively consistent with the collective-pinning theory. Possible pinning natures as well as a possible explanation for the observed Pr concentration dependence of critical current density and activation energy are discussed, especially within the context of pinning induced by the local lattice mismatch due to the Pr doping.