Impurity effects upon the Verwey transition in magnetite

Magnetite single crystals Fe3-xMxO4 doped with M = Ni, Co, Mg;; Al, Ga, and Ti were grown and annealed under a controlled atmosphere to produce homoge neous and oxygen stoichiometric samples. The cation vacancy concentration o f the samples was proved to be lower than 10(-6) by means of magnetic disac commodation spectroscopy; The Verwey temperature shift as function of the s ubstituent concentration was determined from the temperature dependence of the resistivity. The systematics of the transition temperature shift as fun ction of the concentration and nature of the substituents is indicative tha t the mechanism of the transition is related to the second-neighbor Coulomb interaction of the cations on the octahedral sites. [S0163-1829(98)00846-7 ].