Résumé
Time-domain spin resonances in p-doped CdMnTe quantum wells have been studied via time-resolved magneto-optical Kerr rotation. The resonances related to quantum well electrons Mn and electrons excited in the substrate are identified. An additional spin resonance which shows an unusual temperature dependence is detected in one of the samples. The corresponding frequency tends to zero when approaching the Curie temperature. This "soft" spin precession mode has been studied as a function of magnetic field, temperature, magnetic field orientation, and optical excitation density. Its origin is discussed in the framework of the existing collective spin excitation model.