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Intergrain Effects in the AC Susceptibility of Polycrystalline LaFeAsO_{0.94}F_{0.06}

  • Autori: Bonsignore, G; Agliolo Gallitto, A; Li Vigni, M; Luo, JL; Chen, GF; Wang, NL; Shovkun, DV
  • Anno di pubblicazione: 2011
  • Tipologia: Articolo in rivista (Articolo in rivista)
  • Parole Chiave: Oxypnictides; AC susceptibility; Granularity; Josephson junction array
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The AC susceptibility, chi, at zero DC magnetic field of a polycrystalline sample of LaFeAsO_{0.94}F_{0.06} (Tc ≈ 24 K) has been investigated as a function of the temperature, the amplitude of the AC magnetic field (in the range Hac = 0.003 Oe - 4 Oe) and the frequency (in the range f = 10 kHz - 100 kHz). The chi(T) curve exhibits the typical two-step transition arising from the combined response of superconducting grains and intergranular weak-coupled medium. The intergranular part of chi strongly depends on both the amplitude and the frequency of the AC driving field, from few Kelvin below Tc down to T = 4.2 K. Our results show that, in the investigated sample, the intergrain critical current is not determined by pinning of Josephson vortices but by Josephson critical current across neighboring grains.