  In this review, we present a summary of experimental studies of magnetism in
Fe-based superconductors. The doping dependent phase diagram shows strong
similarities to the generic phase diagram of the cuprates. Parent compounds
exhibit magnetic order together with a structural phase transition both of
which are progressively suppressed with doping allowing superconductivity to
emerge. The stripe-like spin arrangement of Fe moments in the magnetically
ordered state shows the identical in-plane structure for the RFeAsO (R=rare
earth) and AFe2As2 (A=Sr, Ca, Ba, Eu and K) parent compounds, notably different
than the spin configuration of the cuprates. Interestingly, Fe1+yTe orders with
a different spin order despite very similar Fermi surface topology. Studies of
the spin dynamics in the parent compounds shows that the interactions are best
characterized as anisotropic three-dimensional (3D) interactions. Despite the
room temperature tetragonal structure, analysis of the low temperature spin
waves under the assumption of a Heisenberg Hamiltonian indicates strong
in-plane anisotropy with a significant next-near neighbor interaction. In the
superconducting state, a resonance, localized in both wavevector and energy is
observed in the spin excitation spectrum as in the cuprates. This resonance is
observed at a wavevector compatible with a Fermi surface nesting instability
independent of the magnetic ordering of the relevant parent compound. The
resonance energy (Er) scales with superconducting transition temperature (TC)
as Er ~4.9 kBTC consistent with the canonical value of ~5 kBTC observed in the
cuprates. Moreover, the relationship between the resonance energy and the
superconducting gap, \Delta, is similar to that observed in many unconventional
superconductors (Er/2\Delta ~ 0.64).
