  We present theoretical aspects of spin polarized two dimensional electron gas
(SP2DEG) which can be achieved in doped semimagnetic quantum wells. This
original model system has been recently studied by magneto Raman scattering
experiments has given a new access to spin resolved excitations and spectrum of
the SP2DEG. Starting from the Diluted Magnetic Semiconductor (DMS) Hamiltonian
in presence of the Coulomb interaction between conduction electrons, we define
the conditions to reach such a SP2DEG. The equilibrium state is studied at low
temperature; in particular a theory for the degree of spin polarization is
derived. Dynamical spin susceptibilities are further calculated in the
framework of a spin density functional formalism already developed in the past.
We then derive spin conserving and spin flip excitations dispersions using a
recent determination of the SP2DEG correlation energy corrected from the
thickness of the well. The SP2DEG presents two key features: the spin flip
wave, which existence is a direct consequence of the Coulomb interaction
between the spin polarized electrons, with a dispersion and energy range
typical to the SP2DEG obtained in DMS, the spin density fluctuations exhibiting
a specific collective behaviour when the spin polarization is increased. The
dissipation spectrum through these excitations is studied in detail. Particular
attention is given to the spectrum determined by resonant Raman scattering. We
show, indeed, that the latter gives unique access to the spin-fluctuations
spectrum of the SP2DEG.
