Using first-principles density functional theory, we have modeled the atomic, electronic and magnetic structure of epitaxial interfaces between the corundum-structure oxides α -Fe_2O3 (hematite) and α -Cr_2O3 (eskolaite) in the hexagonal (0001) basal plane. Our model was a superlattice with a period of about 27.5Åcorresponding to the shortest-period superlattice considered in a recent series of experiments[1]. Two different epitaxial interface structures are possible: (i) an oxygen plane separating an Fe double layer from a Cr double layer, which we refer to as the ``oxygen-divided'' interface; and (ii) a metal double layer split between Fe and Cr, which we call the ``split-metal'' interface. We found that these two structures are close in total energy but have distinct electronic and magnetic structure and different band offsets: 0.4 eV for the oxygen-divided interface and 0.6 eV for the split-metal interface. This may explain the non-commutative band offset seen in the experiments[1] on this system. [1] S. A. Chambers, Y. Liang, and Y. Gao, Phys. Rev. B 61, 13223 (2000).
