Quintuple perovskites Ln2 Ba3 Fe5-x Cox O15-δ (Ln = Sm, Eu) Nanoscale ordering and unconventional magnetism
Abstract
Quintuple perovskites Ln2 Ba3 Fe5-x Cox O15-δ , with Ln = Sm, Eu have been synthesized for x values varying from 0 to 2. The HRTEM and HAADF investigations show that these oxides are ordered at the nanoscale with a tetragonal "ap × ap × 5ap " lattice, corresponding to an ordered fivefold stacking of the Ba and Ln layers. These structures are in fact chemically twinned, so that only cubic or pseudo-cubic symmetry is detected by XRD investigation. The detailed magnetic study shows the existence of short range antiferromagnetic ordering, canted in nature in the temperature range from 5 to 330 K. This particular behavior is interpreted on the basis of local antiferromagnetic M-O-M (M = Fe/Co) interactions within the nanodomains that are limited by pinning of the Co/Fe spins at the boundaries. © The Royal Society of Chemistry.