Impurity Effects on the Transition Temperature of Magnetite

Influence of oxidization and various impurities on the transition temperature of the Verwey order in magnetite was studied experimentally. A small amount of impurities such as Li, Ni, Co, Cr, Al, Ti, Mg, Zn and Ga was doped and the transition temperature was determined by magnetic measurement. The decreases of the transition temperature of the specimens doped with the impurities are not simply related to the amount of the ferrous ions on the B sites but become larger as the ionic configurations deviate from the stoichiometric one. Oxidation of magnetite also decreases the transition temperature and this effect is smaller for the specimens sintered at lower temperature. For the Ga-doped specimens, the concentration dependence of the transition point is found to show a sharp change at a small (0.3%) Ga concentration.