Magnetic properties of doped semiconductors.

Doped semiconductors, being a physical realization of an ensemble of one-electron (hydrogenic) atoms distributed randomly in space, are in a sense the simplest disordered system. Our current understanding of their magnetic properties is reviewed, for densities on both sides of a critical density n sub c at which the system undergoes a transition (at zero temperature) from an insulating phase (n n sub c) to a metallic phase (n > n sub c). It is argued that the insulating phase is well modeled in terms of a disordered Heisenberg antiferromagnet, and quantitative agreement with experiment can be obtained. In contrast, the metallic phase just beyond n sub c, is not as well understood, and a number of possible candidate models are described. Finally, the issue of the effect of magnetic properties on the metal-insulator transition is addressed.