Critical current behavior of superconducting MoN and Mo₃Sb₇ microfibers

We present the transport and critical current measurements on carbon microfibers coated with 40-nm of polycrystalline δ-MoN and on carbon microfibers coated with 160 nm of Mo₃Sb₇. In each case the coatings where synthesized directly onto the 6-μm diameter carbon fibers. The superconducting transition temperature of the MoN microfibers was T_c∼13.1 K, which is the highest temperature reported in any thin film form and is higher than what was reported for stoichiometric δ-MoN, produced by high pressure synthesis. The transition temperature of the Mo₃Sb₇-coated microfibers T_c=7.5 K was significantly higher than that observed in powder samples. Near the transition temperature T_c, the critical current density J_c for both systems was well described by the power-law form [1−(T/T_c)²]^α, where α=1.5 is the Ginzburg–Landau exponent. We extrapolated J_c(0)≈5×10⁷ A/cm² for the MoN microfibers and J_c(0)≈2.5×10⁵ A/cm² for the Mo₃Sb₇ fibers.