Résumé
The structural simplicity of FeCh (Ch=S,Se,Te), in which the conducting layers are not seprated by any third-atom layers, offers the best tool for investigating the nature of superconductivity and magnetism in Fe-based compounds. Either the pressure or the chemical composition distort the FeCh4 tetrahedron and tune the electronic properties. When partially substituting Se for Te in antiferromagnetic Fe1+XTe, the excess of iron is reduced and superconductivity appears over a wide range of compositions. Both the excess iron and Se substitution affect the structure and must be kept under control for tuning the structure deformation and the electronic properties. As a consequence of stretching the FeCh4 thetrahedron, the excess iron is proved to enhance spin and charge localization. Below a critical Fe-Ch distance, the antiferromagnetism is weakened and superconductivity occurs, mediated by spin fluctuationsas in the similar families of Fe_based oxy-pnictides. Uniaxial rather than isostatic pressure has a dramatic effect on the magnetic and superconducting properties of FeCh.