  Time-resolved Kerr rotation measurements were performed in InGaAs/GaAs
quantum wells nearby a doped Mn delta layer. Our magneto-optical results show a
typical time evolution of the optically-oriented electron spin in the quantum
well. Surprisingly, this is strongly affected by the Mn spins, resulting in an
increase of the spin precession frequency in time. This increase is attributed
to the variation in the effective magnetic field induced by the dynamical
relaxation of the Mn spins. Two processes are observed during electron spin
precession: a quasi-instantaneous alignment of the Mn spins with photo-excited
holes, followed by a slow alignment of Mn spins with the external transverse
magnetic field. The first process leads to an equilibrium state imprinted in
the initial precession frequency, which depends on pump power, while the second
process promotes a linear frequency increase, with acceleration depending on
temperature and external magnetic field. This observation yields new
information about exchange process dynamics and on the possibility of
constructing spin memories, which can rapidly respond to light while retaining
information for a longer period.
