High energy spin excitations in BaFe2As2

We report neutron scattering measurements of cooperative spin excitations in antiferromagnetically ordered BaFe2As2, the parent phase of an iron pnictide superconductor. The data extend up to ~100meV and show that the spin excitation spectrum is sharp and highly dispersive. By fitting the spectrum to a linear spin-wave model we estimate the magnon bandwidth to be in the region of 0.17eV. The large characteristic spin fluctuation energy suggests that magnetism could play a role in the formation of the superconducting state.