Long-range antiferromagnetism in Fe-based superconductors

We review neutron scattering studies on the long-range antiferromagnetism in Fe-based superconductors. On cooling from room temperature, most parent compounds of these materials exhibit a tetragonal to orthorhombic/monoclinic structural transition. The system also changes from paramagnetism to a long-range antiferromagnetism. Doping holes or electrons suppresses both transitions and leads to the appearance of superconductivity. We describe the structure and spin wave spectra of various undoped materials, and discuss how the structural and magnetic transitions are affected by the doping.