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 c at which the system undergoes a transition (at zero temperature) from an insulating phase ( n < n c ) to a metallic phase ( n > n 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 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.