VORTEX PINNING IN BI2SR2CACU2O8 TAPES IRRADIATED BY IONS

Vortex pinning due to columnar and point defects was studied in Bi-221 2 tapes irradiated by 230-MeV Au14+ and 120-MeV O7+ ions. Remanent mag netization and critical current density were significantly increased a fter irradiation in the applied field not only perpendicular to but al so parallel to the ab plane. The enhancement of them in the latter fie ld direction was interpreted as kink motion caused by Josephson vortic es across the CuO2 planes. Angular dependence of irreversibility field (H-irr) at 55 K showed line vortices [three dimensional (3D) vortices ] for columnar defects after Au irradiation and it followed the scalin g rule for point defects after O irradiation. The transition of vortic es from 3D to 2D was critically influenced by H-irr namely, by a pinni ng potential.