First principles studies of magnetic oxides, spin-driven ferroelectricity, and the effect of polarization in the chemistry of functional heterointerfaces

Achieving accurate description and understanding of the chemical and physical properties of complex materials enables the further development of their technological applications. Employing density functional theory (DFT) with rotationally invariant Hubbard corrections, we present an extensive study of binary manganese oxides modeling their noncollinear spin patterns and computing their electronic structures in agreement with experimental results. Leveraging on our success in predicting accurately magnetic properties, we explore the noncollinear cycloidal magnetic order in CaMn7O12, which breaks inversion symmetry generating one of the largest spin-driven ferroelectric polarizations measured to date. Based on a generalized spin-current model with Heisenberg-exchange and Dzyaloshinskii-Moriya interaction energetics we explain the microscopic origin of the polarization, including its direction, coupling to the spin helicity, charge density redistribution, and magnetic exchange interactions. Our experimental collaborators synthesize the proposed material, CaMn7O12, in films, reporting experimental evidence of its remarkable high temperature charge ordering phase transition and our atomistic insights through DFT calculations elucidate on the structural and electronic coupling of this phase transition. Symmetry breaking and chemical potential mismatch at an interface could lead to novel phenomena and multifunctional properties inaccessible in the bulk; therefore, interfacial engineering of functional heterostructure geometries could guide devices by design. We propose the functional interface between graphene and polydomain ferroelectrics as platform for novel field effect transistors. Here, we present both a theoretical understanding of how ferroelectric polarization direction affects the graphene carrier density and with help from our experimental collaborators we show evidence of our explanations. We predict that the graphene can be n- or p-type depending on the polari