The angular dependence of the peak effect was investigated in melt-processed (Sm, Eu, Gd)Ba2Cu3O7-δ crystals by rotating the angle, θ, between the applied fields and the ab-plane. The peak field, at which the magnetic moment shows an unusual maximum, shifted to a higher field, associated with a systematical decrease of the peak amplitude with θ inclining to zero. For Ba ∥ ab, the peak effect displayed the highest peak field and the minimum peak height. Meanwhile, out-of-plane ordering of compositional modulation was unveiled by transmission electron microscopy. Such a three-dimensional distribution of chemical fluctuation could account for the angular dependence of the peak effect.
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