This award supports theoretical research on multiferroic materials, which exhibit simultaneous magnetic, electric, and elastic ordering. This project will use a combination of first-principles local-density functional and many-body electronic structure methods to investigate the properties of perovskite-structure manganites as prototypes for this class of materials. The overall goals of the project are to construct a theory of multiferroism, and elucidate the differences between multiferroics and chemically related non-multiferroic materials. Specific problems of interest that will be considered include the origin of the unusual ferromagnetic and ferroelectric behavior of bismuth manganite, the origin of ferroelectricity in antiferromagnetic hexagonal manganites, the coupling between magnetic and ferroelectric order parameters in the manganites, the role of the manganese d electrons in multiferroic behavior, and the effects of the electronic structure on linear and nonlinear optical properties of the multiferroic manganites. The detailed understanding of the fundamental physics underlying multiferroism will assist in the search for new multiferroic materials and in the design of new devices which use them.
Perovskite structure oxides exhibit a broad range of magnetic and electrical properties such as ferroelectric, ferromagnetic, and piezoelectric behavior. This award will support theoretical modeling of a class of such materials denoted as multiferroic, which show simultaneous ferroelectric and ferromagnetic, or ferroelectric and antiferromagnetic ordering. These materials have potential technological application as multiple-state memory elements, electric-field controlled ferromagnetic resonance devices, and transducers with magnetically modulated piezoelectricity. Most multiferroic materials have very complex crystal structures, and as a result both multiferroism and the interrelation of the magnetic, electric polarization, and structural order parameters are note well understood. This project will focus on perovskite-structure manganites exhibiting multiferroism, and investigate these materials using first-principles techniques. The theoretical work supported under this award will also be coordinated with ongoing and new experimental efforts studying multiferroic materials.