Susceptibility of Si:P across the metal-insulator transition. II. Evidence for local moments in the metallic phase

Abstract

For donor concentrations on both sides of the metal-insulator transition, the paramagnetic component of the susceptibility of Si:P at low temperature is described by a power law \ensuremath{\sim}${T}^{\mathrm{\ensuremath{-}}\ensuremath{\alpha}}$, modified by a term which represents thermal activation to higher-energy states which are magnetically inert. For insulating samples, the power law is associated with the random Heisenberg antiferromagnet. The smooth continuation of the same behavior onto the metallic side of the transition suggests that local moments exist in metallic Si:P. We further suggest that this may imply that the exchange interaction between the magnetic moments does not undergo any abrupt or major change in character as the transition is crossed, in spite of the appearance of delocalized electrons.