Atomic-Scale Determination of Cation and Magnetic Order in the Triple Perovskite Sr3Fe2ReO9

Abstract

Pseudo-cubic (pc) perovskite oxides (ABO3) that can have different magnetic cations with different types and degrees of order at B sites have attracted considerable interest as a result of their tunable magnetic properties. Nanoscale inhomogeneity in cation order on the B sites can lead to different magnetic ground states and electronic band structures in local sample regions. Here, we determine cation order on the atomic scale in a nanosized Sr3Fe2ReO9 phase that has a 1:2 B-site-ordered triple perovskite structure using aberration-corrected analytical transmission electron microscopy (TEM), revealing that the Fe and Re cations form tripled-layered repeats with –[Fe–Fe–Re]n– sequences along [111]pc and an ordering vector of 1/3[111]*. To the best of our knowledge, this 1:2 B-site-ordered triple perovskite Sr3Fe2ReO9 phase has not been reported before. Based on a relaxed theoretical model that is consistent with the experimental images, density functional theory calculations are performed to determine the magnetic ground states and exchange parameters of the newly discovered Sr3Fe2ReO9 phase, in which nearest-neighbour Fe and Re cations are coupled antiferromagnetically. This combination of aberration-corrected analytical TEM and ab initio calculations provides physical insight into cation order and magnetic coupling in perovskite oxides at the atomic level.