This research project addresses the magneto-optic response of ZnSe- based quantum well structures incorporating diluted magnetic semiconductor (DMS) layers such as ZnFeSe or ZnMnSe. DMS-based heterostructures are unique among semiconductor quantum wells in that the band offsets between layers can be tuned continuously via the application of an external magnetic field. The project also involves the preparation an study of new magnetic alloys based on zinc, manganese, iron and selenium. The materials can be viewed as two phases, one being a Brillouin paramagnet, the other being a Van Vleck paramagnet. The two phases lead to novel magnetic behavior which can be tuned by varying temperature and the external magnetic field. %%% This research project involves the synthesis and characterization of new semiconducting materials which are also magnetic. These unusual materials have optical properties that vary when they are placed in a magnetic field. These properties offer promise in microwave and information storage technologies.