  Two magnon excitations and the nodal spin density wave (SDW) gap were
observed in BaFe2As2 by Raman scattering. Below the SDW transition temperature
(TSDW) nodal SDW gap opens together with new excitations in reconstructed
electronic states. The two-magnon peak remains above TSDW and moreover the
energy increases a little. The change from the long-range ordered state to the
short-range correlated state is compared to the cuprate superconductors.
