Anomalous magnetization peak effect in spiral-grown Bi2Sr2CaCu2Oy crystals

Magnetic hysteresis loops were measured on spiral-grown Bi2Sr2CaCu2Oy (Bi-2212) crystals. An anomalous peak effect at a magnetic field of 1000–2000 Oe was observed both in high-Tc (86 K) and oxygen underdoped (Tc=76 K) spiral-grown crystals between 20 and 40 K. The peak effect was observed to be stronger than that induced by oxygen vacancies, defect dislocation networks reported in Bi-2212 crystals. Further, the anomalous peak almost completely disappeared after removing growth spiral patterns from the crystal surface. Edge barriers associated with the growth spirals are suggested to be responsible for the strong peak effect for the spiral-grown Bi-2212 crystals and not oxygen vacancies or screw dislocations.