Oxygen Vacancy Ordering and Magnetism in the Rare Earth Stabilised Perovskite Form of “SrCO3-d

We have demonstrated that SrCoO3-d can be stabilised into phase pure perovskite forms by the introduction of small amounts ~5% of certain rare earth ions (Sm3+ - Yb3+). At the same doping levels, La3+ and Pr3+ crystallise with the same isostructural trigonal structure as SrCoO3-d; 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) ap x ap x 2ap superstructure. Strontium and the rare earth ions are disordered over a single site, while the oxygen vacancies are localised on the apical O2 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.