We show that through the resonant optical excitation of spin-polarizedexcitons into CdMnTe magnetic quantum dots, we can induce a macroscopicmagnetization of the Mn impurities. We observe very broad (4 meV linewidth)emission lines of single dots, which are consistent with the formation ofstrongly confined exciton magnetic polarons. Therefore we attribute theoptically induced magnetization of the magnetic dots results to the formationof spin-polarized exciton magnetic polarons. We find that the photo-inducedmagnetization of magnetic polarons is weaker for larger dots which emit atlower energies within the QD distribution. We also show that the photo-inducedmagnetization is stronger for quantum dots with lower Mn concentration, whichwe ascribe to weaker Mn-Mn interaction between the nearest neighbors within thedots. Due to particular stability of the exciton magnetic polarons in QDs,where the localization of the electrons and holes is comparable to the magneticexchange interaction, this optically induced spin alignment persists totemperatures as high as 160 K.
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