  We present a single crystal neutron scattering study of BaMn2Bi2, a recently
synthesized material with the same ThCr2Si2-type structure found in several
Fe-based unconventional superconducting materials. We show long range magnetic
order, in the form of a G-type antiferromagnetic structure, to exist up to 390
K with an indication of a structural transition at 100 K. Utilizing inelastic
neutron scattering we observe a spin-gap of 16meV, with spin-waves extending up
to 55 meV. We find these magnetic excitations to be well fit to a J1-J2-Jc
Heisenberg model and present values for the exchange interactions. The spin
wave spectrum appears to be unchanged by the 100 K structural phase transition.
