Magnetic and ferroelectric properties of Sr1-xBaxMnO3 from first principles

Density functional theory (DFT) calculations are used to study the magnetic and ferroelectric properties of Sr1-xBaxMnO3, with focus on x = 0.5, under isotropic volume expansion or 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 Sr1-xBaxMnO3 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.