Title: Interface magnetism and electronic structure: ZnO(0001)/Co3O4(111),
Abstract: We have studied the structural, electronic and magnetic properties of spinel
$\rm Co_3O_4$(111) surfaces and their interfaces with ZnO (0001) using density
functional theory (DFT) within the Generalized Gradient Approximation with
on-site Coulomb repulsion term (GGA+U). Two possible forms of spinel surface,
containing $\rm Co^{2+} $ and $\rm Co^{3+} $ ions and terminated with either
cobalt or oxygen ions were considered, as well as their interface with zinc
oxide. Our calculations demonstrate that $\rm Co^{3+} $ ions attain non-zero
magnetic moments at the surface and interface, in contrast to the bulk, where
they are not magnetic, leading to the ferromagnetic ordering. Since heavily
Co-doped ZnO samples can contain $\rm Co_3O_4 $ secondary phase, such a
magnetic ordering at the interface might explain the origin of the magnetism in
these diluted magnetic semiconductors (DMS).