Structural characterization, magnetic behavior and high-resolution EELS study of new perovskites Sr2Ru2−xCoxO6−δ (0.5⩽x⩽1.5)
✍ Scribed by A.D. Lozano-Gorrín; J.E. Greedan; P. Núñez; C. González-Silgo; G.A. Botton; G. Radtke
- Publisher
- Elsevier Science
- Year
- 2007
- Tongue
- English
- Weight
- 445 KB
- Volume
- 180
- Category
- Article
- ISSN
- 0022-4596
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✦ Synopsis
New oxides of general formula Sr 2 Ru 2Àx Co x O 6Àd (0.5pxp1.5) have been synthesized as polycrystalline materials and characterized structurally by X-ray diffraction. For 0.5pxo0.67 the orthorhombic, Pnma, perovskite structure of the end member, SrRuO 3 , is found. At x ¼ 0.67 a phase separation into an Ru-rich Pnma phase and a Co-rich I2/c phase occurs. The I2/c form is also found for x ¼ 1.0 but another orthorhombic phase, Imma, obtains for x ¼ 1.33 and 1.5. Reductive weight losses indicate negligible oxygen non-stoichiometry, i.e., d$0, for all compositions even those rich in Co. High-resolution electron energy loss spectroscopy (EELS) indicates that cobalt is high-spin Co 3+ or high-spin Co 4+ for all x. Appropriate combinations of Ru 4+ , Ru 5+ , HS Co 3+ and HS Co 4+ are proposed for each x which are consistent with the observed Ru(Co)-O distances. Significant amounts of Co 4+ must be present for large x values to explain the short observed distances. Broad maxima in the d.c. susceptibilities are found between 78 and 97 K with increasing x, along with zerofield-cooled (ZFC) and field-cooled (FC) divergences suggesting glassy magnetic freezing. A feature near 155 K for all samples indicates a residual amount of ferromagnetic SrRuO 3 not detected by X-ray diffraction.