Magnetic vortices and pinning in thin films and superlattices

Abstract

Thin films and superlattices of high-temperature superconductors (HTS) of the 1:2:3 family are grown by dc magnetron sputtering with different textures. The samples could be grown with the CuO 2 planes parallel to the substrate (the so-called c-axis orientation) or with the CuO 2 planes perpendicular to the substrate (the so-called a-axis orientation). The films are superconducting with critical temperatures ( T c) between 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 EuBa 2Cu 3O 7/PrBa 2Cu 3O 7 (EBCO/PBCO, superconducting/insulating), the T c and J c change with the modulation lengths. These HTS films show very peculiar magnetic properties in the mixed state. The magnetic properties are linked to the behavior of a very soft magnetic vortex lattice and, in the a-axis oriented superlattices, to the competition between natural and artificial anisotropies. In this case, an enhancement of the critical current density J c could be obtained when the magnetic field is applied parallel to the substrate.