200 MeV Ag+15 ion irradiation created columnar defects and enhanced critical current density of La-2125 type superconducting thin films

We have deposited c-axis oriented thin films of La1.5Dy0.5CaBa2Cu5Oz (La-2125) tetragonal superconductor on LaAlO3(001) substrates by pulsed laser deposition. These films were irradiated with 200 MeV Ag+15 ions. Atomic force microscopy and elastic recoil detection analysis indicate that the irradiation has created columnar defects through the entire thickness (2000 Å) of these films. With ion irradiation up to 1×1011 ions/cm2, the critical current density (Jc(H)) enhances by fivefold, which is attributed to the augmented flux pinning by the columnar defects. A further increase in irradiation to 1×1012 ions/cm2 causes reduction in Jc(H) due to distorted morphology of the film. Our work shows that the enhancement in Jc(H) of the irradiated La-2125 film is comparable to that in irradiated RE-123 (RE = rare earth ion). Also, as the La-2125 type films have greater chemical stability than RE-123, La-2125 type superconductors are potential candidates for applications. It is interesting to note that there are partial flux jumps observed to occur symmetrically in the magnetic hysteresis of irradiated La-2125 thin films with enhanced Jc(H).