Scaling behavior of the critical current density in MgCNi3 microfibers
We present transport critical current measurements on microfibers consisting of a 80-nm thick layer of polycrystalline MgCNi3 synthesized directly onto 7-μm diameter carbon fibers. Near the transition temperature Tc, the critical current density Jc is well described by the power law form [1 -(T/Tc)2] α, where α = 2 with no crossover to the Ginzburg-Landau exponent α = 1.5. We extrapolate Jc(0) ≈ 4 × 10 7 A/cm2, which is an order of magnitude greater than estimates obtained from magnetization measurements of polycrystalline powders. The field dependence is purely exponential Jc(T,H)=J c(T)exp(-H/H0) over the entire field range of 0 to 9 T. The unconventional scaling behavior of the critical current may be rooted in an anomalous temperature dependence of the London penetration depth.