Circular Polarization Dynamics during Magnetic Polaron Formation in Type-II Magnetic Quantum Dots

We used time-resolved photoluminescence spectroscopy to study the circular polarization dynamics of magnetic polarons in type-II (Zn,Mn)Te/ZnSe quantum dots in the presence of an external magnetic field. We investigated the time evolution of the peak energy of the sigma(+) and sigma(-) circularly polarized photoluminescence components and of the circular polarization of the emitted light. We also observed that the value of circular polarization, at long delay times, increases with magnetic field. We found that this system exhibits unexpected characteristics, such as different time scales for the formation of the magnetic polaron, on the one hand, and the evolution of photoluminescence circular polarization, on the other hand. These results are discussed within the framework of a theoretical model developed to describe the dependence of magnetic susceptibility as a function of temperature.