  Electron spin relaxation induced by phonon-mediated s-d exchange interaction
in a II-VI diluted magnetic semiconductor quantum dot is investigated
theoretically. The electron-acoustic phonon interaction due to piezoelectric
coupling and deformation potential is included. The resulting spin lifetime is
typically on the order of microseconds. The effectiveness of the
phonon-mediated spin-flip mechanism increases with increasing Mn concentration,
electron spin splitting, vertical confining strength and lateral diameter,
while it shows non-monotonic dependence on the magnetic field and temperature.
An interesting finding is that the spin relaxation in a small quantum dot is
suppressed for strong magnetic field and low Mn concentration at low
temperature.
