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Flux pinning and inhomogeneity in magnetic nanoparticle doped MgB2/Fe wires

A comprehensive study of the effects of magnetic nanoparticle doping on superconductivity and electromagnetic properties of MgB2/Fe wires has been performed. Fe2B and SiO2-coated Fe2B particles with average diameters 80 and 140 nm, respectively, were used as dopands. Two series of MgB2 wires with different nanoparticle contents (0, 3, 7.5, 12 wt.%) were sintered at temperature 750°C. The magnetoresistivity and critical current density Jc of wires were measured in the temperature range 2-40 K in magnetic field B < 16 T. Both transport and magnetic Jc were determined. Superconducting transition temperature Tc of doped wires decrease quite rapidly with doping level (< 0.5 K per wt.%). This results in the reduction of the irreversibility fields Birr(T) and critical current densities Jc(B, T) in doped samples (both at low (5 K) and high temperatures (20 K)). Common scaling of Jc(B, T) curves for doped and undoped wires indicates that the main mechanism of flux pinning is the same in both types of samples. Rather curved Kramer’s plots for Jc of doped wires imply considerable inhomogeneity. The results are compared with the literature reports for the magnetic nanoparticle doping and the probable reasons for the observed behaviour are discussed.

magnesium diboride; magnetic nanoparticle doping; critical current

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