First-principles study of noncommutative band offsets at α-Cr ₂O₃/α-Fe₂O₃(0001) interfaces

Using first-principles density functional theory, we have modeled the atomic, electronic and magnetic structure of epitaxial interfaces between alpha-hematite and alpha-chromia (corundum structure) in the hexagonal (0001) basal plane. Our model was a superlattice with a period of about 27.5 Å, corresponding to the shortest-period superlattice considered in a recent series of experiments [Chambers et al., Phys. Rev. B 61, 13223 (2000)]. Two different epitaxial interface structures were studied: (i) an oxygen plane separating an Fe double layer from a Cr double layer or (ii) a metal double layer split between Fe and Cr. We found that these two structures are close in total energy but have distinct spin structure and different valence band offsets [chromia above hematite by 0.4 and 0.6 eV for (i) and (ii), respectively], possibly explaining the experimental non-commutative band offset seen in this system (0.3±0.1 eV for hematite grown atop chromia, and 0.7 ±0.1 eV for the reverse).