MAGNETIC VORTICES AND PINNING IN THIN-FILMS AND SUPERLATTICES

Thin films and superlattices of high-temperature superconductors (HTS) of the 1:2:3 family are grown by de magnetron sputtering with differe nt textures. The samples could be grown with the CuO2 planes parallel to the substrate (the so-called c-axis orientation) or with the CuO2 p lanes perpendicular to the substrate (the so-called a-axis orientation ). The films are superconducting with critical temperatures (T-c) betw een 85-90 K and with critical currents (J(c)) at 77 K in the range of 10(6) A/cm(2) and 10(5) A/cm(2) for c-axis and a-axis oriented films, respectively. In the case of superlattices of EuBa2Cu3O7/PrBa2Cu3O7 (E BCO/PBCO, superconducting/insulating), the T-c and J(c) change with th e modulation lengths. These HTS films show very peculiar magnetic prop erties in the mixed state. The magnetic properties are linked to the b ehavior of a very soft magnetic vortex lattice and, in the a-axis orie nted superlattices, to the competition between natural and artificial anisotropies. In this case, an enhancement of the critical current den sity J(c) could be obtained when the magnetic field is applied paralle l to the substrate. (C) 1998 Elsevier Science S.A.