Oxygen vacancy ordering and magnetism in the rare earth stabilised perovskite form of "SrCoO3-δ"

We have demonstrated that SrCoO3-delta can be stabilised into phase pure perovskite forms by the introduction of small amounts similar to5% of certain rare earth ions (Sm3+-Yb3+). At the same doping levels, La3+ and Pr3+ crystallise with the same isostructural trigonal structure as Sr6Co5O15; while the Nd3+ composition shows a mixture of both structure types. Powder X-ray diffraction showed only a simple cubic perovskite structure, however, a combination of electron and neutron diffraction has revealed a tetragonal (P4/mmm) a(p) x a(p) x 2a(p) superstructure. Strontium and the rare earth ions are disordered over a single site, while the oxygen vacancies are localised on the apical 02 sites. Magnetisation measurements show that these materials undergo transitions to a spin-glass state at temperatures below 150 K, and that significant coupling occurs between the rare earth ions and the mixed Co3+/(4+) ions. Magnetisation measurements as a function of applied field reveals that below the transition temperature ferromagnetic ordering takes place at relatively large fields. (C) 2004 Elsevier SAS. All rights reserved.