Fully spin-polarized two-dimensional electron gas at the CoFe2O4/MgAl2O4(001) polar interface

We performed first-principles calculations to show that a fully spin-polarized two-dimensional electron gas can be created at the interface between the polar and insulating spinel oxides CoFe2O4 and MgAl2O4. We give a clear description of the physical parameters (in particular the atomic termination of the interfaces), which favor the formation of this electron gas that is due either to an electric field induced in stoichiometric oxide layers because of their polar character or to a charge reorganization that preserves the global electric neutrality in nonstoichiometric layers. We show that the electric field-induced spin-polarized two-dimensional electron gas can only exist if the thickness of the CoFe2O4 layer is large enough and that it may be destroyed by intermixing at the interfaces.