Substitution of magnetic ions in some semiconducting alloys produces materials with interesting properties having high potential for device applications. On the other hand, substitution of specific ions in magnetic materials produces p- or n-type semiconducting properties. In this paper we consider the effects of magnetic ion substitution in the zinc blende structured Hg1−xMnx Te and Cd1−xMnx Te on one hand; and substituted YIG on the other hand. The insulating, extremely low loss characteristics of YIG are drastically changed. Upon substitution. Two models for magnetic loss mechanisms in substituted YIG are presented.