The peak effect (PE) has been observed in a twinned crystal of YBa 2 Cu 3 O 7−δ for H c in the low field range, close to the zero field superconducting transition temperature (T c (0)) . A sharp depinning transition succeeds the peak temperature T p of the PE. The PE phenomenon broadens and its internal structure smoothens out as the field is increased or decreased beyond the interval between 250 Oe and 1000 Oe. Moreover, the PE could not be observed above 10 kOe and below 20 Oe. The locus of the T p (H) values shows a reentrant characteristic with a nose like feature located at T p (H)/T c (0)≈0.99 and H≈100 Oe (where the FLL constant a 0 ≈penetration depth λ). The upper part of the PE curve (0.5 kOe
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