SIMPLE INTERPRETATION OF THE VERWEY TRANSITION IN MAGNETITE

The Verwey transition in magnetite is rationalized in terms of an electronic model involving correlated electron occupancy of nearest‐neighbor octahedral site pairs. This formalism can be restated in terms of order‐disorder theory. The site pair representation of the lattice is analyzed in terms of possible occupation states that represent respectively the ground state of the system as a trapped electron, a first excited state in which an electron can resonate between the two constituents of a site pair, and a second excited state involving two electrons on neighboring sites. The free energy of this representative assembly is then minimized to obtain the equilibrium configuration. The Verwey transition is driven by the Coulomb repulsive interaction between electrons on neighboring sites. In certain limiting cases one obtains results equivalent to the phenomenological Strässler‐Kittel model, which had been successfully used on an empirical basis to analyze both the first‐ and second‐order Verwey transitions that have been experimentally encountered with increasing departures from the ideal 4/3 ratio of oxygen/iron in magnetite. Copyright © 1990, Wiley Blackwell. All rights reserved