FABRICATION AND ELECTRICAL-TRANSPORT PROPERTIES OF EPITAXIAL ND1.85CE0.15CUO4-Y FILMS

Thin films of the electron-doped superconductor Nd1.85Ce0.15CuO4-y (NCCO) have been fabricated on (100) SrTiO3 substrates by inverted cylinder magnetron sputtering. By optimizing the reduction step subsequent to the deposition, superconducting thin films with a transition temperature T-c (R = 0) = 22.5 K and zero-field critical current density J(c) = 1.7 X 10(6) A/cm(2) at T = 4.2 K could be obtained. Also, epitaxial YBCO/NCCO bilayers in which both materials are superconducting could be fabricated. The mixed state of the NCCO films has been characterized by measuring the longitudinal resistivity as well as the Nernst and Seebeck effects in magnetic fields up to 6 T applied parallel to the c-axis. From these measurements an upper critical held slope dB(c2)/dT= - 0.35 T/K was obtained for films with T-c similar or equal to 22 K corresponding to an ab-plane coherence length xi(ab) = 80 Angstrom. The transport energy of magnetic flux lines was derived to dU(phi)/dT = - 2.4 X 10(-13) J/K m. The transport entropy of magnetic flux lines was obtained to S-phi = 1.6 X 10(-14) J/K m at T = 18 K and B = 0.5 T in good agreement with the prediction of time-dependent Ginzburg-Landau theory.