PNNL

Abstract

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 27.5Å, 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).