‘Supercritical’ point on the phase diagram of hematite in an external magnetic field

Abstract

We have calculated a phase diagram, connected with the orientation transitions of hematite (α-Fe 2O 3) at a temperature lower than the Morin point in an external magnetic field, normal to the second-order axis. At the change in the first anisotropy constant corresponding to a decrease in temperature, the phase diagram with the first-order phase transition is transformed into a diagram with two tricritical and one critical points. At a specific temperature (∼ 180 K) these points come together into one ‘supercritical’ point. This point combines the properties of the critical and tricritical points.