Angular dependence of the peak effect and out-of-plane modulated compositional order in melt-processed (Sm, Eu, Gd)Ba₂Cu ₃O_7-δ superconductors

The angular dependence of the peak effect was investigated in melt-processed (Sm, Eu, Gd)Ba₂Cu₃O_7-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 B_a ∥ 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.