A series of new A2MOsO6 osmate double perovskites have been prepared and characterized. All of the compounds studied contain localized electrons and their magnetism is dictated by superexchange interactions.  However, the strength and sign of the superexchange interactions, particularly between 3d transition metal ions and osmium, defy conventional expectations in many cases.  For example in Sr2CoOsO6, the Co(II) and Os(VI) ions order independently despite the fact that the two sublattices are completely interpenetrating.  This suggests that the four bond Os�O�Co�O�Os and Co�O�Os�O�Co superexchange interactions are stronger than the much shorter Os�O�Co superexchange interactions.  This surprising conclusion is supported by DFT calculations.  In Sr2FeOsO6, which contains the d5 high spin Fe(III) ion and the d3 Os(V) ion, the Goodenough-Kanamori rules predict ferromagnetic coupling, but antiferromagnetism is observed.  The behavior of this family of compounds highlights the need for deeper understanding of superexchange interactions in oxides that contain both 3d and 5d transition metal ions.

Osmate double perovskites: A fresh look at magnetism in mixed 5d/3d transition metal oxides

246th National Meeting (2013)

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