Competing spin exchange interactions in Zn1-xMnxSe/Zn1-yFeySe multiple-quantum-well structures

We report the study of a mixed-spin multiple-quantum-well system consisting of alternating Zn1-xMnxSe and Zn1-yFeySe layers, grown by molecular-beam epitaxy. The two spin components of the heavy-hole exciton are each dominated by different exchange interactions as revealed by their temperature and magnetic-field dependence. We find that the energy of the spin-down σ+ component (-3/2,-1/2) is well described by exchange interactions of the electrons and holes with Mn2+ ions (Brillouin paramagnet), while the energy of the spin-up σ- component (+3/2,+1/2) is determined by the interactions of carriers with Fe2+ ions (Van Vleck paramagnet). Thus, these tailored heterostructures permit simultaneous study of Brillouin and Van Vleck paramagnetism as well as associated carrier dynamics in a single structure.