Structure Controlled Magnetism in Mg-Ti-O Thin Films
In Quest of a Ferromagnetic Insulator - Structure Controlled Magnetism in Mg-Ti-O Thin Films Johannes Frantti*,1, Yukari Fujioka1, Christopher Rouleau2, Alexandra Steffen3, Alexander Puretzky2, Nickolay Lavrik2, Ilia N. Ivanov2 and Harry M. Meyer2 1Finnish Research and Engineering, Helsinki 00180, Finland 2Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA 3Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA *Corresponding author: e-mail johannes.frantti@fre.fi 1 Abstract 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, MgTiO3, has an electronic- energy-band structure in which all bands are either full or empty, being a paramagnetic insulator. The MgTiO3 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.
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