Aligned Crystallite Powder of NdFeAsO0.86F0.14: Magnetic Hysteresis and Penetration Depth

Abstract

We report the basal-plane superfluid density and critical current of magnetically aligned NdFeAsO_0.86F_0.14 powder. This sample has individual crystallite grains permanently oriented with their c axis along the external field. The small particles provide a sensitive indicator of dc flux penetration, and allow analysis of the temperature dependence that suggests two-gap characteristics. A quantitative determination of the absolute magnitude is hindered by the need for accurate knowledge of the particle size distribution. Magnetic irreversibilities at high field suggest strong flux pinning of basal-plane critical currents, with monotonic field dependence and no evidence of the �fishtail� effect.