engleski

Vortex Pinning in Nanostructured Novel Superconductors

The influence of magnetic nanoadditives (MN) on electromagnetic properties of MgB2 wires is compared with the effects of nonmagnetic nanoadditives (NN) in bulk MgB2 and with irradiation effects in HTc tapes. Both coated (carbon, silica, or dextrin shell) and uncoated MN were used in order to assess the effects of co-doping and interparticle interaction. Transport and magnetic measurements were used in order to determine connectivity, characteristic fields (Birr, Bc2), and Jc of all wires. Light doping (≤3wt%) enhances Jc and/or Birr for all types of MN, and indicates contribution of magnetic pinning. The enhancement of Jc by the best MN is comparable to that for best NN. In both MN and NN doped MgB2, matching effects in vortex pinning appear causing a maximum enhancement of Birr at higher temperatures, but sizable enhancement persists to the lowest temperatures. Matching effects also appear in irradiated HTc tapes, but with enhancement of Birr limited to vicinity of matching field only. The advantage of enhanced Birr at all temperatures in doped MgB2 wires is practically annulled by poor connectivity.

superconductors ; Vortex pinning ; MgB2

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