INFLUENCE OF TITANIUM DOPING ON THE MAGNETOCRYSTALLINE ANISOTROPY OF MAGNETITE

Magnetization measurements, reported for Fe3-xTixO4 in the composition al range O less-than-or-equal-to x < 0. 04, were used to determine mag netocrystalline anisotropy constants as a function of x and temperatur e. Magnetic measurements were performed along the principal crystallog raphic directions on single-crystalline specimens that had been anneal ed so as to preserve ideal oxygen stoichiometry. In contrast with the differences in the anisotropy of magnetite with Ti substitution, and t hose in nonstoichiometric magnetite above T(V), a remarkable similarit y is observed in the anisotropy constants of Fe3-xTixO4 and Fe3(1-delt a)O4 in their dependence on x and 3delta at T = 4.2 K. At this tempera ture, all anisotropy constants approach zero at the Ti concentration x congruent-to 0. 037, which coincides with the simultaneous disappeara nce of the Verwey transition. Analysis of the results indicates that f or magnetite both Fe2+ and Fe3+ ions contribute to the total anisotrop y energy. The unusual anisotropy constant variation in the temperature range below T(V), observed in the second-order samples, leads to the conclusion, that either some kind of incomplete long-range order is pr esent or that long-range order is entirely missing for x > 0.012.