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The flux pinning mechanism of NdO0.82F0.18FeAs superconductor made under high pressure, with a critical temperature, Tc, of 51 K, has been investigated in detail in this work. The field dependence of the magnetization and the temperature dependence of the magnetoresistivity were measured in fields up to 13 T. The field dependence of the critical current density, Jc(B), was analyzed within the collective pinning model. A crossover field, Bsb, from the single vortex to the small vortex bundle pinning regime was observed. The temperature dependence of Bsb(T) is in good agreement with the delta-l pinning mechanism, i.e., pinning associated with fluctuations in the charge-carrier mean free path, l. Analysis of resistive transition broadening revealed that thermally activated flux flow is found to be responsible for the resistivity contribution in the vicinity of Tc. The activation energy U0/kB is 2000 K in low fields and scales as B (-1/3) over a wide field range. Our results indicate that the NdO0.82F0.18FeAs has stronger intrinsic pinning than Bi-2212 and also stronger than MgB2 for H > 8 T.
We study the temperature dependence of the resistivity as a function of magnetic field in superconducting transition (Tconset - TcR=0) region for different Bi2Sr2CaCu2O8+{delta} superconducting samples being synthesized using sol-gel method. The supe
m-H loops for virgin and neutron irradiated bulk and powder samples of MgB_{2} were measured in the temperature range 5-30 K in magnetic field B<= 1 T. The irradiation at thermal neutron fluences 9*10^{13} and 4.5*10^{14} cm^{-2} caused very small en
Demanding microwave applications in a magnetic field require the material optimization not only in zero-field but, more important, in the in-field flux motion dominated regime. However, the effect of artificial pinning centers (APC) remains unclear a
We have studied flux-pinning effects of MgB$_2$ superconductor by doping (Fe, Ti) particles of which radius is 163 nm on average. 5 wt.% (Fe, Ti) doped MgB$_2$ among the specimens showed the best field dependence of magnetization and 25 wt.% one did
The flux flow properties of epitaxial niobium films with different pinning strengths are investigated by dc electrical resistance measurements and mapped to results derived within the framework of a theoretical model. Investigated are the cases of we