Peak effect with tilted fields in melt-processed (Sm, Eu, Gd)Ba₂Cu₃O_7-δ superconductors

The peak effect in melt-processed (Sm, Eu, Gd)Ba₂Cu₃O_7-δ crystals was investigated by rotating the angle θ, between applied fields, B_a, and the a-b plane. For B_a ∥ c, the scaling of the pinning force over a wide temperature range showed that the predominant pinning is δT_c style pinning. A linear temperature dependence of the peak field, B_p, at which the magnetic moment showed a secondary peak was observed in the magnetic phase diagram. At 85 K, B_p shifted to a higher field, associated with a systematic decrease of the peak amplitude with θ reaching zero. For B_a ∥ ab, the peak effect displayed the highest peak field and the minimum peak height. An ordering compositional fluctuation was observed both in- and out-of-plane by transmission electron microscopy. Such a 3D distribution of chemical variation could account for the angular dependence of the peak effect.