Density Functional Theory Characterization of the Multiferroicity in Spin Spiral Chain Cuprates

The ferroelectricity of the spiral magnets LiCu2O2 and LiCuVO4 was examined by calculating the electric polarizations of their spin spiral states on the basis of density functional theory with spin-orbit coupling. Our work unambiguously reveals that spin-orbit coupling is responsible for the ferroelectricity with the primary contribution from the spin-orbit coupling on the Cu sites, but the asymmetric density distribution responsible for the electric polarization occurs mainly around the O atoms. The electric polarization is calculated to be much greater for the ab- than for the bc-plane spin spiral. The observed spin-spiral plane is found to be consistent with the observed direction of the electric polarization for LiCuVO4, but inconsistent for LiCu2O2.Comment: Phys. Rev. Lett., in prin

Cooperative Effect of Electron Correlation and Spin-Orbit Coupling on the Electronic and Magnetic Properties of Ba2NaOsO6

The electronic and magnetic properties of the cubic double perovskite Ba2NaOsO6 were examined by performing first-principles density functional theory calculations and analyzing spin-orbit coupled states of an Os7+ (d1) ion at an octahedral crystal field. The insulating behavior of Ba2NaOsO6 was shown to originate from a cooperative effect of electron correlation and spin-orbit coupling. This cooperative effect is responsible not only for the absence of orbital ordering in Ba2 NaOsO6 but also for a small magnetic moment and a weak magnetic anisotropy in Ba2NaOsO6