High-energy spin excitations in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mtext>BaFe</mml:mtext></mml:mrow><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mrow><mml:mtext>As</mml:mtext></mml:mrow><mml:mn>2</mml:mn></mml:msub></mml:mrow></mml:math>observed by inelastic neutron scattering

We report neutron-scattering measurements of cooperative spin excitations in antiferromagnetically ordered ${\text{BaFe}}_{2}{\text{As}}_{2}$, the parent phase of an iron pnictide superconductor. The data extend up to $\ensuremath{\sim}100\text{ }\text{meV}$ 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 0.17 eV. The large characteristic spin-fluctuation energy suggests that magnetism could play a role in the formation of the superconducting state.