  The optically induced spin polarization in (Cd,Mn)Te/(Cd,Mn,Mg)Te
diluted-magnetic-semiconductor quantum wells is investigated by means of
picosecond pump-probe Kerr rotation. At 1.8 K temperature, additionally to the
oscillatory signals from photoexcited electrons and Manganese spins precessing
about an external magnetic field, a surprisingly long-lived (up to 60 ns)
nonoscillating spin polarization is detected. This polarization is related to
optical orientation of equilibrium magnetic polarons involving resident holes.
The suggested mechanism for the optical orientation of the equilibrium magnetic
polarons indicates that the detected polaron dynamics originates from unexcited
magnetic polarons. The polaron spin dynamics is controlled by the anisotropic
spin structure of the heavy-hole resulting in a freezing of the polaron
magnetic moment in one of the two stable states oriented along the structure
growth axis. Spin relaxation between these states is prohibited by a potential
barrier, which depends on temperature and magnetic field. The magnetic polaron
relaxation is accelerated with increasing temperature and in magnetic field.
