Double Exchange and the Metal-Nonmetal Transition in Magnetite

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Abstract
A Zener double-exchange model is proposed to account for the electron-hopping process in magnetite. A brief discussion is presented on how such a process might account for some of the well-known electrical-conductivity properties of stoichiometric and nonstoichiometric magnetites. The existence of a metal-nonmetal transition in magnetite is postulated as arising out of the competing contributions to the lattice free energy from orthorhombic ordering and from double exchange. The model is then used to account, qualitatively, for the observed effects of stoichiometry and hydrostatic pressure on the transition temperature.