(a) Supercell for graphene on a (111) BiFeO₃ surface. Gray (the top layer), purple (large), yellow (medium), and red (small) colors represent C, Bi, Fe, and O atoms, respectively. (b) A top view of graphene with one layer of iron atoms. One Fe atom is located at the hollow site labeled by H, while the other two Fe atoms are located at the top sites labeled by A and B. (c) Band structure along high symmetry lines for a 4 × 4 supercell of graphene. Reprinted with permission from Ref. [16]. Copyright 2014 by the American Physical Society.