We show that femtosecond time-resolved optical techniques are ideally suited to excite and probe collective spin
organization and collective spin modes, in diluted magnetic semiconductors based quantum wells. The spin
systems that we consider are low concentration CdMnTe quantum wells, which exhibit various spin phenomena
under optical pulsed excitation, such as spontaneous magnetization patterning, soft mode of magnetization
precession in p-doped quantum wells, and mixed electron-Mn precession in n-doped quantum wells. We examine
also how the carrier-carrier Coulomb interactions affect these collective spin excitations.
The injection of nonequilibrium carriers in a paramagnetic diluted magnetic semiconductor in the presence of magnetic field may induce a spontaneous magnetization patterning. This phenomenon is studied in CdMnTe quantum wells using time resolved Kerr rotation experiments and the model based on the coupled rate equations for interacting electron and magnetic ion spins is developed.