Influence of nonstoichiometry on the Verwey transition.

Abstract

The dependence of the Verwey transition temperature on the nonstoichiometry of ${\mathrm{Fe}}_{3(1\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}})}$${\mathrm{O}}_{4}$ has been characterized by thermomagnetic analysis of the initial permeability in magnetite single crystals subjected to subsolidus controlled oxygen fugacity annealing. Nonstoichiometry depresses the transition temperature, which is a maximum for \ensuremath{\delta}=0. For extreme levels of cation deficiency, a second-order transition occurs at 120 K. An anomaly is reported at 250 K.