Curie Point and Origin of Weak Ferromagnetism in Hematite

Abstract

The Curie point of $\ensuremath{\alpha}$-${\mathrm{Fe}}_{2}$${\mathrm{O}}_{3}$ is found by differential thermal analysis (DTA) to be at 725\ifmmode^\circ\else\textdegree\fi{}C, rather than the value of 675\ifmmode^\circ\else\textdegree\fi{}C known from magnetic measurements. Of the theories on the origin of the weak ferromagnetism in this material, only that of Dzialoshinskii can account for all the experimental data. The 675\ifmmode^\circ\else\textdegree\fi{}C is argued to be a point at which the basal plane anisotropy (assumed nonsymmetric) changes sign.