A route to break molecular nitrogen (N 2 ) under mild conditions is demonstrated by N 2 gas cracking on, and incorporation into, lanthanide films. Successful growth of lanthanide nitride thin films, made by evaporation of lanthanides in a partial N 2 atmosphere at room temperature and pressure as low as 10 –4 Torr, is confirmed using X-ray diffraction. In situ conductance measurements of pure lanthanide thin films exposed to N 2 gas show an immediate surface reaction and a slower bulk reaction. Finally, we report partial reversal of the nitrogen incorporation in a lanthanide nitride by cycling vacuum and nitrogen conditions in the sample chamber.

Single crystals of Ba(Fe1−xNix)2As2 have been produced for systematic magnetic measurements of the critical current density (Jc) over a range of dopings from x = 0.025 to 0.066 and a range of temperatures from 2 K. Analysis of the field dependent critical current density, Jc, shows strong evidence pointing to a flux pinning mechanism dominated by local variation in the mean free path for all dopings. The values of Jc measured indicate a peak at approximately x = 0.049 on the pseudobinary phase diagram, close to a proposed quantum critical point at x = 0.05. Pressure dependent measurements of this sample show anomalous behaviour including a negative pressure relationship and a peak in Jc around 0.65 GPa.

We present the results from structural analysis of single crystalline FeSe1−xTex and magnetisation measurements of as-grown FeSe0.35Te0.65 samples and after they have been annealed in air. Raman spectroscopy revealed that air annealing leads to the formation of hematite (α-Fe2O3) and magnetite (Fe3O4) on the surface of FeSe1−xTex, with the bulk beneath being free of iron oxide. Furthermore, we observe an increase in the superconducting transition temperature, Tc, from 7 to 14 K, and in the critical current density, Jc, by one order of magnitude for all applied magnetic fields. A comparison of two FeSe0.35Te0.65 samples of different thickness indicates a possible size dependence for the optimal annealing conditions. Annealing for a second time (prolonged annealing) was found to induce a surface barrier, indicated by the transition from a symmetric to a highly asymmetric magnetic hysteresis loop.