AC susceptibility and STM studies on Bi 2Sr 2CaCu 2O 8+x single crystals irradiated with heavy ions

Abstract

Three Bi 2Sr 2CaCu 2O 8+ x (BSCCO) single crystals were irradiated with 250 MeV Ag +17 ions, with fluences of 2.5, 5, 10 × 10 10 ions/cm 2 respectively, to create columnar (linear amorphous tracks) type defects in them. The defect structure was characterized at nano level using scanning tunneling microscope (STM) technique. Low ac field ( B ac) magnetic susceptibility measurements, in a frequency range of 0.016–1 kHz and field range of 0.01–10 Gauss, were performed on the crystals before and after the irradiation. Considerable frequency dependence of the susceptibility transitions is observed. Using an Arrhenius-like expression flux creep activation barriers were determined, which show a B ac −0.7 dependence. Introduction of defects leads to a shift of susceptibility transitions to higher temperatures and an increase in activation barrier. The results show the dominance of bulk pinning, rather than surface/geometrical barriers, in determining the flux line dynamics at low fields, and temperatures very near to critical temperature.