Unified model for spin order induced polarization in multiferroics

The microscopic origins of ferroelectricity in different multiferroic systems were theoretically investigated. We proposed a unified model [1,2] which includes purely electronic and ion-displacement contribution simultaneously to describe spin-order induced ferroelectricity. An efficient method [3] was developed to compute the model parameters from first-principles. On the basis of the unified model and density functional calculations, we explained the ferroelectricity induced by the proper-screw spin spiral [2], discovered a novel magnetoelectric coupling mechanism in which the magnitude of the polarization is governed by the exchange striction with the direction by the spin chirality [4], proposed that the ferroelectricity in the chiral-lattice magnet Cu2OSeO3 is due to the unusual single-spin site term [5], unraveled that the magnetoelectric effect observed in BiFeO3 originates from the exchange striction [2].\\[4pt] [1] H. J. Xiang \textit{et al.}, Phys. Rev. Lett. 107, 157202 (2011).\\[0pt] [2] H. J. Xiang \textit{et al.}, Phys. Rev. B 88, 054404 (2013).\\[0pt] [3] H. J. Xiang \textit{et al.}, Phys. Rev. B 84, 224429 (2011).\\[0pt] [4] X. Z. Lu, M.-H. Whangbo, S. Dong, X. G. Gong, and H. J. Xiang, Phys. Rev. Lett. 108, 187204 (2012).\\[0pt] [5] J. H. Yang, Z. L. Li, X. Z. Lu, M.-H. Whangbo, S.-H. Wei, X. G. Gong, and H. J. Xiang, Phys. Rev. Lett. 109, 107203 (2012).