Pillar defects, a new type of track in Pb-irradiated Bi-2212 thin films: Nanostructural study and influence on the irreversibility line

Bi-2212 thin films have been irradiated by 936 MeV Pb ions. An High Resolution Electron Microscopy (HREM) study revealed the formation of square based defects, the so-called pillar tracks, extending throughout the thickness of the film and coexisting with columnar defects of same size. The pinning efficiency of this mixed structure of defects has been investigated by magnetic measurements and compared to a structure containing only columnar defects of the same size. This comparison suggests that pillar defects act the same way as columnar defects of about the same size (125 Angstrom).