The field of this thesis is the new diluted magnetic semiconductors (DMS) with the possibilityof a high Curie temperature : (Ga,Mn)N and (Zn,Cr)Te. Previous studies have shown inboth compounds the same valence d4 for the transition metal ions, and ferromagnetic properties(sometimes paramagnetic for (Ga,Mn)N).A magneto-spectroscopic study on the internal d-d transition of the Mn at 1.4 eV, performedon low Mn content GaN epilayers, less than 0.1%, allowed us to develop a crystal eld modelfor Mn3+ (3d4) including dynamical Jahn-Teller eect. This hypothesis on d4 conguration ofMn is also valid for higher Mn doping, up to a few %. Moreover, magnetic circular dichroism atthe band gap energy, in agreement with the magnetization measurements, has shown a standardDMS with a spin-carrier coupling and a paramagnetic behavior. The measured anisotropy isweaker than the calculated one from the spectroscopic parameters.Magnetization, magnetic circular dichroism and Hall eect measurements have shown ferromagneticproperties with a high disorder. In opposition to standard DMS, the dichroism doesnot come from the absorption at the band gap edge but from a deep band. The ferromagneticstate is not induced by carriers but it is carrier sensitive : a p-type conductivity, obtained withN codoping, suppresses the ferromagnetism, probably because of a change in the Cr valence.
