Influence of deviations from ideal stoichiometry on the anisotropy parameters of magnetite ${\mathrm{Fe}}_{3\left(1\mathrm{-}\mathrm{\delta }\right)}$${\mathrm{O}}_4$

Magnetization measurements are reported for ${\mathrm{Fe}}_{3\left(1\mathrm{-}\mathrm{\delta }\right)}$ ${\mathrm{O}}_4$ in the range 0≤δ<0.010. Anisotropy parameters consistent with these measurements were determined as a function of δ and of temperature T both above and below the Verwey transition temperature. Analysis of the results indicates that the magnetic properties of magnetite are not solely determined by single-ion anisotropies. None of the anisotropy parameters exhibited shifts or slope discontinuities at the critical value ${\delta }_c$, where the Verwey transition undergoes a change in thermodynamic order; this is taken to indicate that the transition is not driven primarily by magnetic interactions.