Faraday spectroscopy in diluted-magnetic-semiconductor superlattices

We investigate the wavelength and magnetic-field dependence of the Faraday rotation in Cd1-xMnxTe/CdTe superlattices in order to probe the strength of the spin-exchange interaction between the excited carriers and the Mn2+ ions in these systems. Using a modulation technique we are able to optically record changes of the density of aligned Mn2+ spin states Sz in the order of Sz/Ssat=6×10-5, where Ssat is the saturation density. We observe a steplike behavior at the absorption edge reflecting the density of states and a strong excitonic resonance, which is difficult to resolve by conventional spectroscopic methods like photoluminescence excitation or transmission spectroscopy. With decreasing barrier width LB we observe below LB=4 nm a decrease of the strength of the spin-exchange interaction indicating the effects of reduced dimensionality. © 1991 The American Physical Society.