Ferromagnetism in diluted magnetic semiconductor heterojunction systems

Diluted magnetic semiconductors (DMSs), in which magnetic elements are substituted for a small fraction of host elements a semiconductor lattice, can become ferromagnetic when doped. In this paper we discuss the physics of DMS ferromagnetism in systems with semiconductor heterojunctions. We focus on the mechanisms that cause of magnetic and magnetoresistive properties to depend on doping profiles, defect distributions, gate voltage and other system parameters that can in principle be engineered to yield desired results. We emphasize that hole densities at the Mn ion locations that exceed 10(20) cm(-3) are a necessary condition for high ferromagnetic transition temperatures in any geometry.