The peak effect in melt-processed (Sm, Eu, Gd)Ba2Cu3O7-δ crystals was investigated by rotating the angle θ, between applied fields, Ba, and the a-b plane. For Ba ∥ c, the scaling of the pinning force over a wide temperature range showed that the predominant pinning is δTc style pinning. A linear temperature dependence of the peak field, Bp, at which the magnetic moment showed a secondary peak was observed in the magnetic phase diagram. At 85 K, Bp shifted to a higher field, associated with a systematic decrease of the peak amplitude with θ reaching zero. For Ba ∥ 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.
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