  The magnetic microstructure and domain wall distribution of antiferromagnetic
$\alpha$-Fe$_2$O$_3$ epitaxial layers is determined by statistical image
analyses. Using dichroic spectro-microscopy images, we demonstrate that the
domain structure is statistically invariant with thickness and that the
antiferromagnetic domain structure of the thin films is inherited from the
ferrimagnetic precursor layer one, even after complete transformation into
antiferromagnetic $\alpha$-Fe$_2$O$_3$. We show that modifying the magnetic
domain structure of the precursor layer is a genuine way to tune the magnetic
domain structure and domain walls of the antiferromagnetic layers.
