Magnetic anisotropy of titanomagnetites ${\mathrm{Fe}}_{3\mathrm{-}\mathit{x}}$${\mathrm{Ti}}_{\mathit{x}}$${\mathrm{O}}_4$, 0≤x≤0.55

Magnetization measurements reported for ${\mathrm{Fe}}_{3\mathrm{-}\mathit{x}}$ ${\mathrm{Ti}}_{\mathit{x}}$ ${\mathrm{O}}_4$ in the composition range 0≤x≤0.55 were used to determine the magnetic-anisotropy coefficients as a function of x and of temperature. Magnetic measurements were performed along the principal crystallographic directions in applied fields up to 15 kOe and in the temperature range 4.2 to 300 K on single-crystalline specimens that had been annealed so as to preserve the ideal oxygen stoichiometry. Magnetic-anisotropy parameters were calculated from magnetization curves and analyzed in terms of estimated magnetoelastic contributions to the magnetic anisotropy, with use of published magnetostriction and elastic-constant data. The anisotropy constant ${\mathit{K}}_1$ passes through a minimum at x=0.2, irrespective of temperature, at a composition where ${\mathrm{Fe}}^{2+}$ first begins to appear in tetrahedral interstitial sites; ${\mathit{K}}_1$ grows rapidly with increasing x for x>0.2. The results show that the magnetoelastic contribution to the magnetic anisotropy dominates at high x and originates from the presence of ${\mathrm{Fe}}^{2+}$ Jahn-Teller ions on the tetrahedral sublattice. Within the large theoretical uncertainties, the variation of ${\mathit{K}}_1$ with temperature could be adequately reproduced by the theory.