THE EFFECT OF SAMPLE SHAPE ON THE MAGNETIZATION IN BI2SR2CACU2O8+DELTA CRYSTALS

Magnetic moment measurements have been made on differently shaped sing le crystals of Bi2Sr2CaCu2O8+delta using a SQUID magnetometer. In plat elet shaped samples, the results show a pronounced geometrical barrier (GB) or 'shape effect' at low fields and high temperatures. In both p rism and semi-ellipsoidal-shaped samples, the low field magnetic hyste resis is reduced significantly at high temperatures due to modificatio n of the geometrical barrier. At lower temperatures, the prism and sem i-ellipsoidal samples show enhanced low field hysteresis relative to t he platelet, suggesting an increasing role of nongeometrical surface b arriers (SB). These results are discussed in terms of the competing ro les of bulk pinning, surface and geometrical barrier effects. (C) 1998 Elsevier Science B.V. All rights reserved.