  We have measured dispersions of spin-flip waves and spin-flip single-particle
excitations of a spin polarized two-dimensional electron gas in a CdMnTe
quantum well using resonant Raman scattering. We find the energy of the
spin-flip wave to be below the spin-flip single particle excitation continuum,
a contradiction to the theory of spin waves in diluted magnetic semiconductors
put forth in [Phys. Rev. B 70, 045205 (2004)]. We show that the inclusion of
terms accounting for the Coulomb interaction between carriers in the spin wave
propagator leads to an agreement with our experimental results. The dominant
Coulomb contribution leads to an overall red shift of the mixed electron-Mn
spin modes while the dynamical coupling between Mn ions results in a small blue
shift. We provide a simulated model system which shows the reverse situation
but at an extremely large magnetic field.
