The doping dependence of the irreversibility line in grain-aligned Sm1−xEuxBa2Cu3O7−δ high-Tc superconductor

The irreversible properties of a rare-earth high-Tc superconductor are investigated using grain-aligned Sm1-xEuxBa2Cu3O7−δ (x = 0.0, 0.3, 0.5, 0.7, and 0.9) samples. The samples were synthesized using the usual solid–state reaction method. It is found that the transition temperature Tc and the critical current density Jc calculated by the Bean model are significantly improved in the optimally doped samples (x = 0.5 and 0.7). Furthermore, the double logarithmic graph of the irreversibility line Birr in the grain-aligned series samples obeys approximately a power law dependence n(1−T/Tc)(1−T/Tc)n. Results show that in the case of optimally doped samples with x = 0.5 and 0.7 the graph of Birr is fitted well with the relation n(1−T/Tc)(1−T/Tc)n with the model-dependent parameter n ∼1.5 without any crossover in the entire temperature range, while in samples with x = 0.0, 0.3, and 0.9 Birr does show a prominent crossover and can be characterized with n ∼1.5 only near Tc, above which Birr varies more rapidly. Finally, it is suggested that Birr is strongly dependent on the extrinsic properties of our grain-aligned samples.