Temperature-dependent collective pinning exponent in Bi2Sr2Ca2Cu3O10+x tapes and bulk samples with preferential crystallite orientation

The low-voltage-level current-voltage characteristics of Bi₂Sr₂Ca₂Cu₃O_10+x tapes and bulk samples with preferential crystallite orientation were measured in applied magnetic fields both parallel and perpendicular to the samples' surfaces. The data were interpreted within the framework of the collective pinning model. The collective pinning exponent changes from 1 to 0.5 (close toT _c), while in the case of unoriented samples it is constant (and equal to the theoretical value 1/2) as shown in an earlier paper. We suggest that this temperature dependence of is due to the change of the dimensionality of the intragranular vortices.