Pinning mechanism in electron-doped HTS Nd 1.85 ?> Ce 0.15 ?> CuO 4 − δ ?> epitaxial films

The electrical transport properties of c-axis oriented Nd1.85Ce0.15CuO4 − δ superconducting films have been investigated to analyze the pinning mechanism in this material. The samples were grown on SrTiO3 substrates using the dc sputtering high-pressure technique, whereas a detailed analysis of the structure and local composition of the films has been achieved using high-resolution electron microscopy and x-ray microanalysis. Magneto-resistance and current-voltage measurements, in the temperature range from 1.6 to 300 K and in magnetic field up to 9 T, have been reported. In particular, the anisotropic coefficient defined as the ratio between the parallel upper critical field, H c 2 ∥ ?> ab, and the perpendicular one, H c 2 ∥ ?> c, has been evaluated, pointing out the high anisotropy of this compound. Furthermore, the vortex activation energy as a function of the applied magnetic field, parallel and perpendicular to the CuO2 planes, has been derived and compared with the flux-pinning forces to enlighten the peculiar nature of pinning centers in this material.

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