Neutron Scattering Study of CoO_6 Distortion and Its Relation to the Spin-State Transition in Pr_<0.5>Ca_<0.5>CoO_3(Condensed matter: electronic structure and electrical, magnetic, and optical properties)

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This study compares the electrical resistivity, magnetization, and high-resolution neutron powder diffraction data obtained for Pr_<0.5>Ca_<0.5>CoO_3 and Pr_<0.5>Ca_<0.5>CoO_<3-δ> (δ〜0.045). Although both samples exhibit similar structural parameters, the distortion of the CoO_6 octahedra is weaker in Pr_<0.5>Ca_<0.5>CoO_<3-δ> than in Pr_<0.5>Ca_<0.5>CoO_3 at low temperatures. This reduced distortion decreases the electron-lattice coupling, which increases the itinerant nature of the e_g electrons in the oxygen-deficient sample. In addition, the oxygen deficiency can add Co^<3+> ions into Pr_<0.5>Ca_<0.5>CoO_<3-δ>, yielding an increased population of e_g electrons. As a result, the sharp spin-state transition observed in Pr_<0.5>Ca_<0.5>CoO_3 is suppressed in Pr_<0.5>Ca_<0.5>CoO_<3-δ>, which exhibits a lower magnitude of resistivity and stronger magnetism at low temperatures.
社団法人日本物理学会の論文
2009-03-15