We show that features of the dynamical spin susceptibility can unambiguously distinguish between different pairing symmetries of the superconducting state in iron-based superconductors. A magnetic resonance is a feature for the extended $s_{x^2{y}^2}$-wave $\text{cos}{k}_x\text{cos}{k}_y$ pairing symmetry. It is present in the pure superconducting (SC) state but weakens in the mixed SC and magnetically ordered state. We calculate the random-phase approximation correction to the NMR spin-relaxation rate $1/T_1$ and the Knight shift in the above states and show a good agreement with experimental results. Moreover, we argue that the energy dispersion of the magnetic resonance along the $c$ axis observed in neutron scattering experiments is also an indirect evidence supporting the $s_{x^2{y}^2}$ pairing symmetry.

• Received 13 March 2009

DOI:https://doi.org/10.1103/PhysRevB.79.235207