INFLUENCE OF TITANIUM DOPING ON THE MAGNETOCRYSTALLINE ANISOTROPY OF MAGNETITE

Magnetization measurements, reported for Fe3-xTixO4 in the compositional range O less-than-or-equal-to x < 0. 04, were used to determine magnetocrystalline anisotropy constants as a function of x and temperature. Magnetic measurements were performed along the principal crystallographic directions on single-crystalline specimens that had been annealed so as to preserve ideal oxygen stoichiometry. In contrast with the differences in the anisotropy of magnetite with Ti substitution, and those in nonstoichiometric magnetite above T(V), a remarkable similarity is observed in the anisotropy constants of Fe3-xTixO4 and Fe3(1-delta)O4 in their dependence on x and 3delta at T = 4.2 K. At this temperature, all anisotropy constants approach zero at the Ti concentration x congruent-to 0. 037, which coincides with the simultaneous disappearance of the Verwey transition. Analysis of the results indicates that for magnetite both Fe2+ and Fe3+ ions contribute to the total anisotropy 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 present or that long-range order is entirely missing for x > 0.012.