Electric polarization of Sr${}_{0.5}$Ba${}_{0.5}$MnO${}_3$: a multiferroic Mott insulator

Abstract

Ab initio calculations of the electric polarization of correlation-driven insulating materials, namely Mott insulators, have not been possible so far. Using a combination of density functional theory and dynamical-mean-field theory we study the electric polarization of the Mott insulator Sr${}_{0.5}$Ba${}_{0.5}$MnO${}_3$. We predict a ferroelectric polarization of $\simeq 16.5\mu C/c{m}^2$ in the high temperature paramagnetic phase and recover the measured value of $\simeq 13.3\mu C/c{m}^2$ in the low temperature antiferromagnetic phase. Our calculations reveal that the driving force for the ferroelectricity, the hybridization between Mn e${}_g$ and O p orbitals, is suppressed by correlations, in particular by the Hund coupling and by the onset of magnetic order. They also confirm that the half-filled Mn $t_{2g}$ orbitals give rise to the antiferromagnetic Mott phase. This magnetic ordering leads to changes in the ionic polar displacement and in turn to the electronic polarization. In addition, for a fixed ionic displacement, we find that there is a reduction in the electronic contribution due to partial magnetic polarization of the Mn e${}_g$ orbitals. The reduction of the polarization due to ionic displacement dominates over the additional electronic part, hence the net magneto-electric coupling is negative.

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Cited by in corpus (2)

• Correlation-driven electronic multiferroicity in (TMTTF)${}_2$-$X$ organic crystals
• Magnetic and ferroelectric properties of Sr${}_{1-x}$Ba${}_x$MnO${}_3$ from first principles