  The possibility of magnetic-order induced phonon anisotropy in single
crystals of MnO and NiO is investigated using inelastic neutron scattering.
Below Tn both compounds exhibit a splitting in their transverse optical phonon
spectra of approximately 10%. This behavior illustrates that, contrary to
general assumption, the dynamic properties of MnO and NiO are substantially
non-cubic.

Strongly Correlated Electrons