Carrier spin polarization in digital Mn/GaAs ferromagnetic structures studied with hot electron photoluminescence

The effect of ferromagnetic layers on the spin polarization of holes and electrons in digital Mn/GaAs ferromagnetic heterostructures (DFHs) is studied with hot electron photoluminescence. We show that carriers in the GaAs interlayers experience a strong exchange interaction with the ferromagnetic interfaces. This exchange field rapidly decreases with increasing distance between the ferromagnetic Mn $\ensuremath{\delta}$ layers. The relaxation of the ferromagnetic properties of the digital structures is caused by compensation of the holes mediating the ferromagnetism of DFHs by electrons originating from the GaAs interlayers. For comparison, the polarization of holes in granular MnAs:GaAs, which consists of MnAs nanocrystals embedded in a GaAs matrix, is also studied. In this case, the holes in the GaAs matrix do not experience any strong magnetic fields from the ferromagnetic MnAs nanocrystals.