Strong flux pinning in nano-SiC doped MgB2 tapes
Irreversibility fields Birr and critical current densities Jc of undoped and doped (10 wt% SiC) MgB2/Cu tapes and MgB2/Fe wires were measured from 2 K up to 38 K in magnetic field B □ 16 T. For B □ 1 T, Birr(T) variation for all samples is similar, but Birr of MgB2/Fe is higher than that of corresponding MgB2/Cu tapes. However, the enhancement of Birr upon doping, Birr(dop.)/Birr(undop.) ≈ 1.4 is the same for both types of samples indicating the same pinning mechanism. Birr of doped MgB2/Fe wire reaches that of optimised NbTi wires (10 T, 4.2 K) already at 20 K and extrapolates to 21 T at 4.2 K (close to that of Nb3Sn). In spite of low core density (~1.2 g/cm3) Jc of doped MgB2/Fe wire is high and decreases little with magnetic field: Jc(4.2 K) = 19 kA/cm2 in B = 13 T which yields FP = JcB = 2.5 GN/m3. Since Jc and Jc-B variation in our samples is limited by core porosity and defects (cracks and voids), the Jc and FP values for more dense and homogeneous SiC doped samples are probably several times larger.