Energy and spin relaxation of excitons in CdMnTe/CdMgTe quantum wells

The energy and spin relaxation of excitons and trions is studied in the (Cd, Mn)Te/(Cd,Mg)Te quantum wells containing hole magnetic polarons by means of polarized photoluminescence technique. It was found that under circularly polarized photoexcitation with an energy higher than the ground state energy of the exciton, photoluminescence is also polarized. This fact points to the presence of the spin memory of the excitons in these systems. It is suggested that the long spin memory is due to the magnetic polaron formation stabilizing the spin of the exciton. Under quasiresonant excitation of the trion states an inverted sign of circular polarization degree is observed in the radiation spectrum. Such inversion of the polarization degree requires the special mechanism of the spin relaxation, associated with the spin flip of an electron in the trion magnetic polaron state. Application of the external magnetic field in the Voigt geometry leads to the depolarization of the excitonic radiation. The cause of this depolarization is the destabilization of the magnetic polaron and the shortening of the spin relaxation time of the exciton. •Long spin memory in (Cd, Mn)Te/(Cd, Mg)Te QWs is due to the magnetic polaron formation stabilizing the spin of the exciton.•Negative circular polarization degree of the photoluminescence obtained under quasiresonant photoexcitation.•The origin of the negative circular polarization of photoluminescence is attributed to the magnetic polaron state.•The suggested model of NCP is based on the spin relaxation asymmetry of the electron in the magnetic polaron state.