COEXISTENCE OF BRILLOUIN AND VANVLECK SPIN-EXCHANGE IN ZN1-XMNXSE ZN1-YFEYSE SPIN SUPERLATTICE STRUCTURES

We have studied a new type of semiconductor quantum well system in whi ch the carrier-ion exchange interactions are determined by the spin of the carrier. The samples consist of alternating layers of Zn1-xMnxSe and Zn1-yFeySe grown by molecular-beam epitaxy (MBE). At zero field, t he carriers initially interact randomly with both transition metal spe cies. When a magnetic field is applied, the excitonic wave functions a re increasingly localized in one or the other of the magnetic layers a ccording to their spin state as the competing spin exchange interactio ns define the confining potential. The spin components of the heavy ho le exciton are subsequently dominated by different exchange interactio ns as revealed by their temperature and field dependence: the behavior of the spin-down component (-3/2,-1/2) is described by exchange inter actions of the carriers with the Mn2+ ions and exhibits Brillouin para magnetic behavior, while the spin-up component (+3/2,+1/2) is dominate d by interactions with Fe2+ ions and exhibits Van Vleck paramagnetism. These structures are thus characterized-by an initial competition and eventual coexistence of Brillouin- and Van Vleck-like paramagnetic be havior for the exciton.