Ž . Thin Solid Films 317 1998 285–289 Magnetic vortices and pinning in thin films and superlattices J.I. Martın a , M. Velez a , E.M. Gonzalez b , J.L. Vicent a, ) ´ ´ ´ a Departamento Fisica de Materiales, Facultad de Fisicas, UniÕersidad Complutense, Madrid 28040, Spain b Departamento Propiedades Opticas, Magneticas y de Transporte, Instituto de Ciencia de Materiales, CSIC, Cantoblanco, Madrid 28049, Spain Abstract Ž . Thin films and superlattices of high-temperature superconductors HTS of the 1:2:3 family are grown by dc magnetron sputtering Ž . with different textures. The samples could be grown with the CuO planes parallel to the substrate the so-called c-axis orientation or 2 Ž . with the CuO planes perpendicular to the substrate the so-called a-axis orientation . The films are superconducting with critical 2 Ž . Ž . 6 2 5 2 temperatures T between 85–90 K and with critical currents J at 77 K in the range of 10 Arcm and 10 Arcm for c-axis and c c Ž a-axis oriented films, respectively. In the case of superlattices of EuBa Cu O rPrBa Cu O EBCOrPBCO, superconductingrinsulat- 2 3 7 2 3 7 . ing , the T and J change with the modulation lengths. These HTS films show very peculiar magnetic properties in the mixed state. The c c 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 could be obtained c when the magnetic field is applied parallel to the substrate. q 1998 Elsevier Science S.A. Keywords: Thin films; Superlattices; Magnetron sputtering 1. Introduction Thin films of the 1:2:3 family of oxide cuprates could be grown by different vacuum deposition techniques, as laser ablation, molecular beam epitaxy, etc.; but, among them, the sputtering method allows us to grow good-qual- ity films and multilayers with different textures. The grow- ing conditions to obtain films of HTS are very extreme, since very high substrate-temperature during deposition wx and high-oxygen pressure in the chamber are required 1 . Therefore, magnetron sputtering seems to be a useful technique. Laser ablation could produce good quality films too; but in this case, the surface roughness could be a problem if multilayers have to be fabricated. The mixed state behavior of HTS has been one of the wx most interesting topics in the field 2 . A magnetic field applied to a HTS leads to many new phenomena, most of them due to the combination of the short vortex core size Ž . small coherence length and the structural anisotropy of these oxide cuprates. Another topic related with basic and applied research is the behavior of the critical current J in c the vortex state. The pinning mechanisms of the vortices should be understood in a way to enhance the J values, c ) Corresponding author. which is very important from the technological point of view. In this paper we will present the fabrication of thin Ž . films of EuBa Cu O EBCO and superlattices of 2 3 7 Ž EuBa Cu O r PrBa Cu O superconducting 2 3 7 2 3 7 Ž . Ž .. EBCO rinsulating PBCO with different textures. The so-called a-axis oriented films and superlattices allow us to study the interplay between the natural pinning of the magnetic vortices due to the cuprate structure and the artificial pinning due to the PBCO insulating layers. 2. Experimental results The films and superlattices have been grown in a commercial dc magnetron sputtering system, using stoi- Ž . chiometric targets and on 100 SrTiO substrates. The 3 system is computer-controlled and the substrate holder can be moved in front of each target to grow the multilayers. The substrate–target geometry is on-axis and the technique wx is the same described in Ref. 3 used to grow c-axis Ž oriented samples. c-axis oriented films CuO planes par- 2 . allel to the substrate are the usual texture reported in the Ž literature, a-axis oriented films CuO planes perpendicu- 2 . lar to the substrate need very strict conditions to grow 0040-6090r98r$19.00 q 1998 Elsevier Science S.A. All rights reserved.