The field of this thesis is the new diluted magnetic semiconductors (DMS) with the possibility of a high Curie temperature : (Ga,Mn)N and (Zn,Cr)Te. Previous studies have shown in both 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, performed on low Mn content GaN epilayers, less than 0.1%, allowed us to develop a crystal eld model for Mn3+ (3d4) including dynamical Jahn-Teller eect. This hypothesis on d4 conguration of Mn is also valid for higher Mn doping, up to a few %. Moreover, magnetic circular dichroism at the band gap energy, in agreement with the magnetization measurements, has shown a standard DMS with a spin-carrier coupling and a paramagnetic behavior. The measured anisotropy is weaker than the calculated one from the spectroscopic parameters. Magnetization, magnetic circular dichroism and Hall eect measurements have shown ferromagnetic properties with a high disorder. In opposition to standard DMS, the dichroism does not come from the absorption at the band gap edge but from a deep band. The ferromagnetic state is not induced by carriers but it is carrier sensitive : a p-type conductivity, obtained with N codoping, suppresses the ferromagnetism, probably because of a change in the Cr valence.
Magneto-optical study of (Ga,Mn)N and (Zn,Cr)Te