  Spins of charge carriers, paramagnetic centers, and nuclei in semiconductor
structures are known to be oriented if circular-polarized light is shined upon
the structure. This is due to transfer of angular momentum from photons to
various excitations in the semiconductor. What would happen if the structure is
anisotropic, so that the angular momentum is not conserved? Experiments
performed on diluted-magnetic II-VI quantum wells (such as CdMnTe/CdMgTe) show
that at some conditions the effect of light upon the spin state of the
semiconductor structure can be greatly amplified. Exchange field of
photoexcited heavy holes initiates a coherent evolution of a great number of
localized spins of Mn-ions. In the simplest case, it is just a precession in an
effective field, but generally the spin dynamics is more intricate. It shows
up, for instance, in long sequences of spin-flip peaks in Raman spectra, in
enhanced magnetic-polaron effect, and in modulation of optical response within
the picosecond time scale.
