Dielectric properties and spin-phonon coupling in multiferroic double perovskite Bi${}_2$CoMnO${}_6$

Abstract

First-principles electronic structure calculations have been performed for the double perovskite Bi${}_2$CoMnO${}_6$ in its non-centrosymmetric polar state using generalized gradient approximation plus Hubbard U approach. We find that while Co is in a high spin state, Mn is in an intermediate spin state. The calculated dynamical charge tensors are anisotropic reflecting a low-symmetry structure of the compound. Magnetic structure dependent phonon frequencies indicate the presence of spin-phonon coupling. Using Berry phase method, we obtain a spontaneous electronic polarization of 5.88 $\mu C/c{m}^2$ which is close to the experimental value observed for a similar compound, Bi${}_2$NiMnO${}_6$.

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