G. D. Loos

METAL-INSULATOR TRANSITION IN SRRUO3 INDUCED BY ION IRRADIATION

We have studied the effect of He+ irradiation on the electrical resistivity and Curie temperature of ferromagnetic SrRuO3 thin films. An evolution from metallic to insulating behavior is observed when He+ ion fluence is increased, suggesting a metal-insulator transition. Damage by ion irradiation produces a strong decrease of the Curie temperature. On the other hand, no significant change in T-c (similar to 160 K) takes place in fresh samples grown at different substrate temperatures. We discuss the possible correlation between structural changes induced by irradiation, which reflect in an increase of the pseudocubic lattice parameter, and the observed depression of T-c.

Critical temperature depression and persistent photoconductivity in ion irradiated YBa2Cu3O7-x films and YBa2Cu3O7-x/PrBa2Cu3O7 superlattices

We have studied the effect of He+ irradiation with doses in the range 1012–2×1015 cm−2 on two high-temperature superconducting structures: YBa2Cu3O7−x (YBCO) films and YBa2Cu3O7−x/PrBa2Cu3O7 (YBCO/PBCO) superlattices. In particular we have focused on superlattices [YBCON/PBCOM]1000 A with N=1, 8 unit cells of YBCO, and M=5 unit cells of PBCO, with a total thickness of 1000 A. The analysis is presented in terms of depression of the critical temperature (Tc) and modification of the crystalline structure using X ray refinement technique. Single films show a systematic increase in the c-lattice parameter upon irradiation, which is not observed in thin one unit cell YBCO layers in superlattice structures. However, Tc depression resulting from irradiation is deeper in superlattices. These results are explained considering the strained nature of the as-grown [YBCON/PBCO5]1000 A superlattices with low values of N. Both structures show persistent photoconductivity, indicating that defects are related to oxygen dis...

Chain oxygen disorder in deoxygenated YBa2Cu3O7-δ thin films induced by light ion irradiation

Abstract We report on the effects of light ion (He + ) irradiation on the superconducting properties of epitaxial YBa 2 Cu 3 O 7− δ thin films. Films were grown by a pure oxygen dc sputtering system operated at high pressure (3.4 mbar). Irradiation at 80 keV and doses ranging between 10 14 and 10 15 cm −2 shows a systematic degradation of the superconducting transition temperature. We have studied the effects of annealing on the recovery of the superconducting properties of films irradiated at different fluences. Two sets of irradiated samples were evaluated, fully oxidized and deoxygenated samples. Irradiated fresh samples do not show significant recovery upon room temperature annealing for times as long as 6 months. Irradiated deoxygenated samples, however, show an up to 10 K increase in the critical temperature after 2 months room temperature annealing. The different behavior is discussed in terms of the two effects caused by irradiation: oxygen displacements from the CuO chains into stable interstitial positions along the a -axis, and oxygen disorder in the deoxygenated samples.