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 10 00-2000 Oe was observed both in high-T-c (86 K) and oxygen underdoped (T-c = 76 K) spiral-grown crystals between 20 and 40 K. The peak effec t was observed to be stronger than that induced by oxygen vacancies, d efect dislocation networks reported in Bi-2212 crystals. Further, the anomalous peak almost completely disappeared after removing growth spi ral patterns from the crystal surface. Edge barriers associated with t he 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.