Exciton-controlled magnetization in single magnetic quantum dots

We report on low temperature polarization-resolved imaging of single magnetic self-assembled CdMnTe quantum dots (QDs) in the absence of magnetic field. Using longitudinal optical phonon-assisted absorption to photoexcite spin-polarized excitons into a QD ground state, we find that the magnetic impurities within CdMnTe QDs can be aligned ferromagnetically with a single emission lines exhibiting a circular polarization as large as 65%. These results demonstrate that the magnetization of a single magnetic QD can be optically controlled with a suitably polarized laser.