ENHANCED VORTEX-PINNING STRENGTH AND MAGNETIC-IRREVERSIBILITY VIA COLUMNAR DEFECTS IN SINGLE-CRYSTAL BI2SR2CACU2O8

To enhance vortex pinning in the high-T(c) superconductor Bi2Sr2CaCu2O 8, single crystals were irradiated with energetic heavy ions to create columnar defects. Irradiations were made at various angles from the c -axis. The Pinning energy U0 was investigated by ac magnetometry near B(T(irr)), the limit of quasistatic magnetic irreversibility. Irradiat ion increased U0 by a factor of approximately 3, relatively independen t of the ion-beam exposure, which increased both J(c) and the irrevers ible B-T regime. Independence of J(c) and U0 from the magnetic-field o rientation suggests the predominance of strong pins interacting with 2 -D pancake vortices.