  To resolve the microscopic origin of magnetism in the Fe2O3/FeTiO3-system, we
have performed density functional theory calculations taking into account
on-site Coulomb repulsion. By varying systematically the concentration,
distribution and charge state of Ti in a hematite host, we compile a phase
diagram of the stability with respect to the end members and find a clear
preference to form layered arrangements as opposed to solid solutions. The
charge mismatch at the interface is accommodated through Ti4+ and a
disproportionation in the Fe contact layer into Fe2+, Fe3+, leading to
uncompensated moments in the contact layer and giving first theoretical
evidence for the lamellar magnetism hypothesis. This interface magnetism is
associated with impurity levels in the band gap showing halfmetallic behavior
and making Fe2O3/FeTiO3 heterostructures prospective materials for spintronics
applications.
