First-principles study of improper ferroelectricity in TbMnO3

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  • 28 March 2008
Abstract
We have carried out a first-principles theoretical study of the magnetically induced polarization in orthorhombic TbMnO3, a prototypical material in which a cycloidal spin structure generates an electric polarization via the spin-orbit interaction. We compute both the electronic and the lattice-mediated contributions to the polarization and find that the latter is strongly dominant. We analyze the spin-orbit induced forces and lattice displacements from both atomic and mode-decomposition viewpoints, and show that a simple model based on nearest Mn--Mn neighbor Dzyaloshinskii-Moriya interactions is not able to account fully for the results. The magnitude of our computed polarization is in fairly good agreement with experiment, but questions remain concerning the sign.

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