Oxygen vacancy ordering and magnetism in the rare earth stabilised perovskite form of 'SrCoO_(3-δ)'

摘要

We have demonstrated that SrCoO_(3-δ) can be stabilised into phase pure perovskite forms by the introduction of small amounts ～5% of certain rare earth ions (Sm~(3+)-Yb~(3+)). At the same doping levels, La~(3+) and Pr~(3+) crystallise with the same isostructural trigonal structure as Sr_6Co_5O_(15); while the Nd~(3+) 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×a_p×2a_p superstructure. Strontium and the rare earth ions are disordered over a single site, while the oxygen vacancies are localised on the apical O_2 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 Co~(3+/4+) ions. Magnetisation measurements as a function of applied field reveals that below the transition temperature ferromagnetic ordering takes place at relatively large fields.