Properties of alpha-Fe2O3
Alpha Fe2O3 has rhombohedral structure which can be described using hexagonal axis.
Structure
Space group: R -3 c (167), a corundum structure.
Magnetism
Neel temperatures
TN=948 K
TM=260K
Spin structure:
Above TM, the spins axis is along [1-10]hex direction, as shown in the figure.
Below TM, the spin axis is along [001]hex direction.
The transition at TM=260K is called Morin transition. Basically, the crystallographic anisotropy constant changed. The c-axis becomes easy axis below TM.
Another detail is that the spins alignment is antiferromagnetic (AFM), but above the Morin transition, the spins are slightly tilted, resulting a weak ferromagnetim moment in ab plane. It is believed that this canting is coming from the DM interaction. Below Morin transition, this canted moment is gone.