The modulation of the peak effect in melt-processed (Sm-Eu)123 superconductors with compositional fluctuations

The peak effect in magnetization loops of melt-processed (Sm_xEu_1-x)Ba₂Cu₃O_7-δ superconductors is manipulated by varying the Sm/Eu ratio in the initial composition. In all the samples the peak field B_p(T), at which the magnetization moment reaches the maximum, was linearly temperature dependent. The fitting to such a relationship unveils a slightly lower critical temperature T_cp than the bulk T_c at zero field. A kink appears in the reversible magnetization moment of the field dependence of superconducting transition. This kink temperature T_ck(B) is also a linear function of applied field. Transmission electron microscopy (TEM) observation confirms the presence of nano-scale regular compositional modulation arising from local RE-Ba substitution, which is weakened with increasing Eu concentration. The peak effect is thus attributed to the scattering of local T_c due to compositional fluctuation.