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A quantum kinetic theory of the spin transfer between carriers and Mn atoms in a Mn doped diluted magnetic semiconductor is presented. It turns out that the typical memory time associated with these processes is orders of magnitude shorter than the time scale of the spin transfer. Nevertheless, Markovian rate equations, which are obtained by neglecting the memory, work well only for bulk systems. For quantum wells and wires the quantum kinetic results qualitatively deviate from the Markovian limit under certain conditions. Instead of a monotonic decay of an initially prepared excess electron spin, an overshoot or even coherent oscillations are found. It is demonstrated that these features are caused by energetic redistributions of the carriers due to the energy-time uncertainty.

InSb and InMnSb samples have been investigated by means of magneto-optical Kerr effect and magnetic circular dichroism. In binary semiconductor compounds such as InSb the observed magneto-optical spectra exhibit narrow and distinct resonances which can be associated with dipole-allowed transitions between the Landau levels in conduction and valence bands. With increasing magnetic field the Landau splitting increases and the observed peaks change their position and amplitude accordingly. In contrast to this observation, the magneto-optical spectra of the diluted magnetic semiconductor InMnSb show only one strong and broad resonance. Contrary to what one expects, particularly in narrow gap materials with large g factors and small effective masses, the shape and position of this resonance do not change with the applied magnetic field. It is found, however, that the amplitude depends linearly on the magnetization of the samples. In this paper we describe how these observations can be understood by means of a k ជ · p ជ theory incorporating the exchange interaction of free carriers with localized electrons in the Mn ions.

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