FLUX-PINNING BY COLUMNAR DEFECTS IN HIGH-TEMPERATURE SUPERCONDUCTING CRYSTALS

Y-Ba-Cu-O:123 and Bi-Sr-Ca-Cu-O:2212 crystals were irradiated with 5.8 GeV Pb ions. The columnar defects, produced by this irradiation are e xpected to yield the strongest possible pinning energy. Indeed, there is an apparent increase in the width of the magnetization curves. Howe ver, the results of magnetic relaxation experiments indicate the energ y barrier for flux creep from the columnar defects much smaller than e xpected pinning energy. This effect is explained in terms of nucleatio n of vortex loop mechanism of flux creep. The estimate of pinning ener gy of columnar defect can be obtained from measurement of the angular dependence of the magnetization curves..