Quintuple perovskites Ln2Ba3Fe5−xCoxO15−δ (Ln = Sm, Eu): nanoscale ordering and unconventional magnetism

Abstract

Quintuple perovskites Ln₂Ba₃Fe_5−xCo_xO_15−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 “a_p × a_p × 5a_p” 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.