Superconducting and magnetotransport properties of ZnNNi3 microfibers and films
We present the superconducting and critical current properties of ZnNNi3 in the form of annularly coated carbon microfibers and thin films. The fibers were prepared by heating 6-8μm diameter commercially available Ni-coated carbon fibers with Zn powder in a flowing stream of NH3 gas at 650°C. The fibers had a Tc =3.75K, which was slightly higher than that of the polycrystalline powder and an upper critical field, Hc2 (0) =0.92T. Near the transition temperature Tc, the critical current density Jc was well described by the Ginzburg-Landau power-law form [1- (T/ Tc) 2] 3/2. The extrapolation produces Jc (0) ≅1.45× 106 A/ cm2. An axial magnetic field produces an exponential decrease in the critical current density. Planar ZnNNi3 films were formed on sapphire substrates by exposing thin Ni films to a similar heat treatment as the fibers. Hall measurements on the films in the normal state revealed a carrier density, n=-1.46× 1023 cm-3. © 2009 The American Physical Society.