1 Max-Planck-Institut für Festkörperforschung, Heisenbergstraße 1, 70569 Stuttgart, Germany
2 Laboratoire Léon Brillouin, CEA-CNRS, CEA Saclay, 91191 Gif-sur-Yvette, France
3 Forschungsneutronenquelle Heinz Maier-Leibnitz (FRM-II), TU München, D-85747 Garching, Germany
In March 2008, superconductivity at high critical temperature (Tc> 50K) was found in iron-arsenide compounds  to the surprise of the scientific community. Indeed, the magnetic iron was rather regarded as an antagonist of superconductivity. Moreover, it is the first time that a so high critical temperature is reached without copper. Very like copper oxide superconductors, these new superconductors have a lamellar structure with layers of iron and "pnictures" (compounds of As, P. .., that are elements of the 15th column of the Mendeleyev table) which are interposed between plans of "charge reservoirs" (see figure). These materials also present a phase diagram similar to that of cuprates with, versus the doping concentration, an antiferromagnetic phase adjacent to the superconducting zone ( ).