  We propose paramagnetic semiconductors as active media for refrigeration at
cryogenic temperatures by adiabatic demagnetization. The paramagnetism of
impurity dopants or structural defects can provide the entropy necessary for
refrigeration at cryogenic temperatures. We present a simple model for the
theoretical limitations to specific entropy and cooling power achievable by
demagnetization of various semiconductor systems. Performance comparable to
that of the hydrate (CMN) is predicted.
