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Vortex pinning by correlated disorder in nanoparticle doped MgB2

Magnetoresistivity and critical current density were measured on five Si-nanoparticle doped (c<=10 wt.%) and undoped Cu-sheathed MgB2 tapes and wires for temperatures T>=28 K in magnetic fields B<=0.95 T. Unlike the irreversibility lines Birr(T) for undoped samples (smooth lines), Birr(T) for doped samples shows a change in slope which is typical for high-temperature superconductors (HTS) with correlated disorder. Microstructural studies of nanoparticle doped MgB2 show uniforlmy dispersed Mg2Si nanopercipitates which probably act as a correlated disorder (Bphi is the matching field). But, in contrast to HTS, in nanoparticle doped MgB2 the enhancement of Birr (with respect to undoped one) persists at all field scales (including B>>Bphi).

vortex; correlated disorder; nanoparticle doped; MgB2; magnetoresistivity; critical current density

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