Metal--Insulator Transitions in Pyrochlore Oxides Ln2Ir2O7

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概要

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• We report the physical properties of Ln2Ir2O7 (Ln = Nd, Sm, Eu, Gd, Tb, Dy, and Ho), which exhibit metal--insulator transitions (MITs) at different temperatures. The transition temperature T_{\text{MI}} increases with a reduction in the ionic radius of Ln. The ionic radius boundary for MITs in Ln2Ir2O7 lies between Ln = Pr and Nd. MITs in Ln2Ir2O7 have some common features. They are second-order transitions. Under the field cool condition, a weak ferromagnetic component ({\sim}10^{-3} \mu_{\text{B}}/f.u.) caused by Ir 5d electrons is observed below T_{\text{MI}}. The entropy associated with MITs for Ln = Nd, Sm, and Eu is estimated to be 0.47, 2.0, and 1.4 J/(K\cdotmole), respectively. The change in entropy is much smaller than 2R\ln 2 [11.5 J/(K\cdotmole)] expected in a magnetic transition due to localized moments of S = 1/2. The feature of continuous MITs in Ln2Ir2O7 is discussed.

• 2011-09-15

著者

• Wakeshima Makoto

  Division Of Chemistry Graduate School Of Science Hokkaido University

• Hinatsu Yukio

  Division Of Chemistry Graduate School Of Science Hokkaido University

• TAKAGI Seishi

  Faculty of Engineering, Kyushu Institute of Technology

• MATSUHIRA Kazuyuki

  Faculty of Engineering, Kyushu Institute of Technology

• Matsuhira Kazuyuki

  Faculty of Engineering, Kyushu Institute of Technology, Kitakyushu 804-8550, Japan

• Hinatsu Yukio

  Division of Chemistry, Graduate School of Science, Hokkaido University, Sapporo 060-0810, Japan

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