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

M Eisterer,J Karpinski,S Katrych,N D Zhigadlo,V Mishev,M Zehetmayer

doi:10.1088/0953-2048/27/4/044009

Abstract

We report on angle-resolved magnetization measurements on NdFeAsO0.65F0.35 (Nd-1111) single crystals. The field dependence of the critical current density, Jc, is non-monotonic in these crystals at all orientations and temperatures due to the fishtail effect, which strongly influences the angular dependence of Jc. 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 Jc 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 Jc can be described via anisotropic scaling only after an appropriate extension to this pinning regime.

Highlights

The pinning properties of iron-based superconductors have been a focus of intensive research since the discovery of superconductivity in these compounds [1]
We report on angle-resolved magnetization measurements on NdFeAsO0.65F0.35 (Nd-1111) single crystals
In this study we report on the anisotropy of the in-plane critical currents of Nd-1111 single crystals by means of angle-resolved magnetization measurements

Summary

Introduction

The pinning properties of iron-based superconductors have been a focus of intensive research since the discovery of superconductivity in these compounds [1]. The critical currents in single crystals often show a fishtail effect, which disappears after the introduction of an efficient pinning landscape, for instance by irradiation techniques [2,3,4,5,6,7]. Angle-resolved measurements of the pinning properties are very efficient for studying the pinning landscape and anisotropy effects of the vortex lattice. They have been performed nearly exclusively on films so far, in which growth-related and often correlated defects dominate the properties, which are not representative for the defects prevailing in bulk materials such as single crystals or grains in wires or tapes. Thin films are widely available only for the Ba-122 (BaFe2As2) [8,9,10,11,12,13,14,15] and 11 (FeSe1−xTex) [16,17,18,19,20] families and only a few data exist for

Results

Discussion

Conclusion