Schematic densities of states of (a) EuO and (b) GdN. (c) Side view of the proposed interface structure composed of one GdN layer atop one EuO layer on a SrO substrate. Large atoms are cations (Gd, Eu, and Sr), and small atoms are anions (N and O). Reprinted with permission from Ref. [27]. Copyright 2014 by the American Physical Society.