Magnetic characterization of polycrystalline NdFeAsO0.88F0.12 oxypnictide superconductor

The superconducting properties of polycrystalline NdFeAsO0.88F0.12 oxypnictide were studied by both DC and AC magnetization measurements. The zero-field cooled (ZFC) magnetic susceptibility, χ(T), measured under the magnetic field of 0.5 T shows a dramatic decrease at about 11 K. The imaginary component of the first harmonics of the AC magnetic susceptibility, χ″(T), increases with the increasing DC field Hdc below 11 K. These results indicate the onset of robust intergranular superconductivity at low temperatures. The magnetic hysteresis loops show an anomalous double central peak effect at low temperatures, with one peak at positive fields in decreasing positive external fields. This phenomenon suggests the granular character of this system. The paramagnetism of Nd3+ ions tilts the magnetic hysteresis loops and broadens the hysteresis width ΔM. After correction for the paramagnetism, the temperature and field dependence of the average magnetization critical current density Jcm was obtained. The related mechanism was discussed.

Research highlights▶ Then onset of intergranular superconductivity was detected by DC and AC susceptibility. ▶ A double-peak effect and the central peak shift were observed in the M(H) curves. ▶ The experimental results confirm the granularity nature. ▶ The influence of paramagnetism of Nd3+ ions on magnetization Jc was investigated.