Microscopic origin of large negative magneto-electric coupling in Sr$_{1/2}$Ba$_{1/2}$MnO$_{3}$

TL;DR

This study reveals that in Sr$_{1/2}$Ba$_{1/2}$MnO$_{3}$, the large negative magneto-electric coupling arises from polar distortions stabilized by Mn-O hybridizations, with magnetic interactions strongly influenced by bond-bending distortions.

Contribution

The paper introduces a new mechanism linking polar distortions and magnetic superexchange, explaining the strong magnetoelectric coupling in this manganite.

Findings

Polar distortion stabilized by Mn-O hybridization.

Magnetic superexchange highly sensitive to bond-bending.

Reduced ferroelectric polarization observed with magnetic ordering.

Abstract

With a combined ab initio density functional and model Hamiltonian approach we establish that in the recently discovered multiferroic phase of the manganite Sr$_{1/2}$Ba$_{1/2}$MnO$_{3}$ the polar distortion of Mn and O ions is stabilized via enhanced in-plane Mn-O hybridizations. The magnetic superexchange interaction is very sensitive to the polar bond-bending distortion, and we find that this dependence directly causes a strong magnetoelectric coupling. This novel mechanism for multiferroicity is consistent with the experimentally observed reduced ferroelectric polarization upon the onset of magnetic ordering.