Probing the Links between Structure and Magnetism in Sr2鈥?i>xCaxFeOsO6 Double Perovskites

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• 作者：Ryan Morrow ; John W. Freeland ; Patrick M. Woodward
• 刊名：Inorganic Chemistry
• 出版年：2014
• 出版时间：August 4, 2014
• 年：2014
• 卷：53
• 期：15
• 页码：7983-7992
• 全文大小：505K
• ISSN：1520-510X

文摘

The synthesis, structure, and properties of the ordered double perovskites Sr₂FeOsO₆, Ca₂FeOsO₆, and SrCaFeOsO₆ are reported. The latter two compounds have monoclinic P2₁/n symmetry and a^{鈥?/sup>a鈥?/sup>b+ tilting of the octahedra, while Sr₂FeOsO₆ is tetragonal with I4/m symmetry and a0a0c鈥?/sup> tilting. Magnetic measurements indicate and neutron powder diffraction studies confirm that Ca₂FeOsO₆ is a ferrimagnet with a Curie temperature of 350 K. The ferrimagnetism is retained if half of the Ca2+ ions are replaced with larger Sr2+ ions to form SrCaFeOsO₆ (T_C = 210 K). This substitution reduces the degree of octahedral tilting, but unlike most perovskites, the magnetic ordering temperature decreases as the Fe鈥揙鈥揙s bond angles approach a linear geometry. In contrast, Sr₂FeOsO₆ orders antiferromagnetically, as previously reported. X-ray absorption spectroscopy confirms the assignment of Fe(III) and Os(V) oxidation states for all three compounds. In these insulating double perovskites, the magnetic ground state is governed by a competition between the four-bond Fe鈥揙鈥揙s鈥揙鈥揊e antiferromagnetic superexchange coupling of Fe(III) ions and the two-bond Fe鈥揙鈥揙s antiferromagnetic superexchange coupling between neighboring Fe(III) and Os(V) ions. When the Fe鈥揙鈥揙s bonds are linear, as they are in the c direction in Sr₂FeOsO₆, the four-bond coupling between Fe(III) ions prevails. The competition shifts in favor of antiferromagnetic coupling of Fe(III) and Os(V) as the Fe鈥揙鈥揙s bond angles bend in response to chemical pressure.}