engleski

Flux-pinning and inhomogeneity in MgB_2/Fe wires

Transport critical current densities J_c and irreversibility fields B_irr of undoped and nanoparticle doped (10 wt% SiC) Fe-sheathed MgB_2 wires were measured from 2 to 40K in magnetic field B<16T. For the best segments of wires (<1 cm)both the magnitude and field variations of J_c and the pinning force density F_p=J_cB depend only on the magnitude of B_irr, hence the strength of flux-pinning. B_irr of doped wire for T<30K is ~1.4 times larger than that of undoped and reaches that of NbTi (10T at 4.2K) already at 20K. Accordingly, its high-field J_c s and F_p s are large, typically three times larger than the best literature results, and are limited by the porosity and inhomogeneity of the superconducting cores in present-day MgB_2 wires.

superconductors; flux pinning and creep

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