  Ferromagnetic insulator thin films can convey information by spin waves,
avoiding charge displacement and Eddy current losses. The sparsity of
high-temperature insulating ferromagnetic materials hinders the development of
spin wave based devices. Stoichiometric magnesium titanate, MgTiO$_3$, has an
electronic-energy-band structure in which all bands are either full or empty,
being a paramagnetic insulator. The MgTiO$_3$ ilmenite consists of ordered
octahedra and cation network in which one third of the octahedra are vacant,
one third host magnesium and one third titanium. By giving up these
characteristics, a rich variety of different magnetic structures can be formed.
Our experiments and electronic-energy-band-structure computations show that the
magnetic and electric properties of Mg-Ti-O films can drastically be changed
and controlled by Mg- and Ti-cation arrangement and abundancy in the octahedra.
Insulating titanium- and semiconducting magnesium-rich films were ferromagnetic
up to elevated temperatures. The presence and origin of ferromagnetic
insulating phase in the films is not apparent - the expectation, based on the
well-established rules set by Goodenough and Kanamori, is paramagnetic or
antiferromagnetic ordering. We show that ferro- and paramagnetic phases,
possessing the same stoichiometry, can be obtained by merely rearranging the
cations, thus allowing defect-free interfaces in multilayer structures.

Materials Science;Applied Physics