  We measured phonon frequencies and linewidths in doped and undoped BaFe2As2
single crystals by inelastic x-ray scattering and compared our results with
density functional theory (DFT) calculations. In agreement with previous work,
the calculated frequencies of some phonons depended on whether the ground state
was magnetic or not and, in the former case, whether phonon wavevector was
parallel or perpendicular to the magnetic ordering wavevector. The experimental
results agreed better with the magnetic calculation than with zero Fe moment
calculations, except the peak splitting expected due to magnetic domain
twinning was not observed. Furthermore, phonon frequencies were unaffected by
the breakdown of the magnetic ground state due to either doping or increased
temperature. Based on these results we propose that phonons strongly couple not
to the static order, but to high frequency magnetic fluctuations.
