Critical current anisotropy in Nd-1111 single crystals and the influence of neutron irradiation

Abstract

We report on angle-resolved magnetization measurements on NdFeAsO 0.65 F 0.35 (Nd-1111) single crystals. The field dependence of the critical current density, J c , is non-monotonous in these crystals at all orientations and temperatures due to the fishtail effect, which strongly influences the angular dependence of J c . The currents decrease as the field is tilted from the crystallographic c-axis at low fields, but increase at high fields. A peak occurs in the angular dependence of J c at intermediate fields. The critical currents are significantly enhanced after irradiation with fast neutrons and the fishtail disappears. The different current anisotropies at low and high fields, however, persist. We discuss the data in the framework of the anisotropic scaling approach and propose a transition from dominant pinning by large defects of low density at low fields to pinning by small defects of high density at high fields in the pristine crystal. Strong pinning dominates at all fields after the irradiation, and the angular dependence of J c can be described by anisotropic scaling only after an appropriate extension to this pinning regime.

Fe-based superconducting thin films on metallic substrates: Growth, characteristics, and relevant properties

“…(c) Fe(Se,Te) on Fe-buffered MgO prepared by PLD23 and Fe 1+y Te 0.6 Se 0.4 single crystal 24. (d) NdFeAs(O,F) on MgO fabricated by MBE 25 and single crystal 26.…”

Emergence of superconductivity in single-crystalline LaFeAsO under simultaneous Sm and P substitution

“…6(b) and 6(c), respectively. We note that the estimated critical current densities, jc, are slightly lower than those of single-crystalline iron-pnictide superconductors with Tc ~ 40 K [55,56]. This is not surprising, considering that, the upper-and the lower critical fields of our crystals are smaller than those of the iron-pnictide counterparts and that the pinning is proportional to the thermodynamic critical fields.…”

Anisotropic field dependence of the electronic transport in superconducting FeSe thin films

“…The B * c2 anisotropy in figure 10 is of particular importance. For a number of iron-based superconductors, namely NdFeAsO 0.65 F 0.35 (Nd-1111) [81], LaFeAsO 1−x F x (La-1111) [58], Ba(Fe 1−x Co x ) 2 As 2 (Ba-122) [82], and Fe(Se,Te) (11) [83], it was shown that the single-band scaling approach by Blatter et al [84] properly describes the angular dependences B * c2 (ϑ), B c2 (ϑ), and j c (ϑ) also for a multiband system. When ϑ is the angle that makes the applied field B with the c-axis (ϑ = 0 • for B II c and ϑ = 90 • for B II ab), B * c2 (ϑ) is related to the ratio of the effective masses of the effective charge carriers m c along the c-axis and m ab in the ab-plane through the equation…”