Aligned crystallite powder of NdFeAsO\(_{0.86}\)F\(_{0.14}\): magnetic hysteresis and penetration depth

We report the basal-plane critical current and superfluid density of magnetically aligned NdFeAsO\(_{0.86}\)F\(_{0.14}\) powder. This sample has individual crystallite grains permanently oriented with their c axis along the external field. 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. The small particles provide a sensitive indicator of \textit{dc} flux penetration, and allow analysis of the temperature dependence of \(ab-\)plane London penetration depth \(\lambda_{ab,\mathrm{L}}\), which is quadratic at low \(T\). This feature may not necessarily be due to the nodes in the gap, but may be rather a sign of a strong pair-breaking. A quantitative determination of the absolute magnitude of \(\lambda_{ab,\mathrm{L}}\) is hindered by the need for accurate knowledge of the particle size distribution.