EFFECT OF HE+ IRRADIATION ON THE MAGNETIC-PROPERTIES OF SUPERCONDUCTING YBA2CU3O7 THIN-FILMS

Irradiation induced defects have been thought to create strong pinning centres leading to high critical current density J(c) of YBaCuO. We report here for the first time, the effect of He+ ion irradiation on J(c) and T(c) of laser ablated epitaxial thin films of YBaCuO (approximately 100 nm) on (100) SrTiO3, studied through magnetization and transport measurements. J(c) (H = O) of the unirradiated film (T(c) approximately 89 K) at 10 K decreases rapidly from 3.25 x 10(7) A/cm2 to 0.9 x 10(7) A/cm2 for the film with 5 x 10(15)/cm2 dose. While T(c) has a nearly stable value (upto 2 x 10(15)/cm2 dose), J(c) contrary to neutron irradiation studies, drops by a factor of more than three, followed by a slower decrease. Transport measurements also corroborate such behaviour. One possible mechanism of vortex pinning in thin films could be the surface pinning. In this case the initial decrease in J(c) with He+ irradiation could be due to a decrease in surface pinning while at high dose level, the film quality appears to have deteriorated (T(c) approximately 81 K) possibly due to a change of oxygen stoichiometry. Various possibilities are examined to explain the observed results.