Fabrication and Superconducting Properties of Alternately-layered MgB_2/Ni Thin Films with Different Ni-layer Spacing

We will show the superconducting properties of alternately-layered MgB2/Ni thin films inserted as very thin (1 nm) nickel layers between MgB2 layers a few tens of nanometers thick. The MgB2/Ni thin films were prepared on silicon (100) substrates by sequentially switching electron-beam evaporation and coaxial vacuum arc evaporation techniques without post-annealing. In this study, we prepared alternately layered MgB2/Ni thin films with varying Ni-layer spacings. The Ni layer spacings were set to 32, 23 and 16 nm, respectively. The MgB2/Ni thin films were neither inter-diffusion nor chemical reactions between MgB2 and Ni. Clear enhancements of the Jc were observed in the MgB2/Ni thin films when the magnetic fields were applied parallel to the inserted Ni layers, and the peak positions in the Fp–B curves shifted to higher magnetic fields with the decrease of the Ni-layer spacing. These results clearly indicate that the Ni layers inserted in alternately-layered MgB2/Ni thin films work as very effective flux-pinning centers.