Magnetic and ferroelectric properties of Sr$_{1-x}$Ba$_{x}$MnO$_3$ from first principles

TL;DR

This study uses first-principles calculations to explore how Ba substitution affects the magnetic and ferroelectric properties of SrMnO3, revealing complex interactions between electronic structure, volume changes, and strain.

Contribution

It provides new insights into the effects of Ba substitution on magnetic exchange interactions and ferroelectric polarization in SrMnO3 from a first-principles perspective.

Findings

Ba substitution enhances magnetic exchange interactions at fixed lattice parameters.

Volume expansion from Ba weakens magnetic interactions, leading to suppressed magnetism.

Ferroelectric properties are mainly influenced by volume expansion, with significant magnetoelectric coupling.

Abstract

Density functional theory (DFT) calculations are used to study the magnetic and ferroelectric properties of Sr$_{1-x}$Ba$_{x}$MnO$_3$, with focus on $x=0.5$, under isotropic volume expansion/compression and biaxial strain. Our results indicate that, unexpectedly, Ba substitution alters the electronic structure in a way that, at fixed lattice parameter, notably enhances the interatomic magnetic exchange interactions. However, increasing Ba-content also causes a volume expansion which tends to weaken these interactions, leading to a net effect of weakly suppressed magnetism, as observed in experiments. The ferroelectric properties, on the other hand, are found to be less affected by changes in the electronic structure and can largely be understood in terms of the volume expansion caused by Ba-substitution. The calculated electric polarization as a function of biaxial strain in Sr$_{1-x}$Ba$_{x}$MnO$_3$ for $x=0$ and $x=0.5$, shows that the difference between the two is mainly due to differences in the magnetic order at certain strain values, accompanied by enormous magnetoelectric coupling.