  We present the results of a comprehensive magneto-optical characterization of
single CdTe quantum dots containing a few Mn2+ ions. We find that some quantum
dots exhibit an unexpected evolution of excitonic photoluminescence spectrum
with the magnetic field. At a certain value of the magnetic field, specific for
every quantum dot, each of the broad spectral lines related to the
recombination of various excitonic complexes confined inside the dot transforms
into a pair of narrow lines split by several meV. We interpret this abrupt
change in the character of excitonic emission spectrum as a consequence of a
transition from a non-polarized state of the Mn2+ spins in a low field regime
to a highly (almost fully) polarized state above the critical magnetic field.
Various optical experiments, including polarization-resolved studies,
investigation of different excitation regimes and time-resolved measurements
corroborate this scenario. However, these measurements indicate also that the
observed effect is not related or influenced by the photo-created charge
carriers, but it is rather originating from unusual spin configuration in the
cluster of Mn2+ ions.
