Simple microscopic model of the magneto-electric effect in non-collinear magnets
Abstract
A 2-site 2-electron model with s- and p-states on each site, having constrained average site-spins Sa, Sb, with angle theta between them, simpler than the previous closely-related model of Katsura et al (KNB), is considered. Intra-site Coulomb repulsion and inter-site spin-orbit coupling V(SO) are included. The ground state has an electric dipole moment pi consistent with the result of KNB, pi proportional to R x (Sa x Sb) = f, R connecting the two sites, and application to a spiral leads to ferroelectric polarization with direction f, also in agreement with the previous result. However, the present result shows the expected behavior pi goes to 0 as V(SO) goes to 0, unlike the previous one.
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