Heavy-Mass Behavior of Ordered Perovskites ACu_3Ru_4O_<12> (A=Na, Ca, La)(Condensed matter: electronic structure and electrical, magnetic, and optical properties)

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We synthesized ACu_3Ru_4O_<12> (A=Na, Na_<0.5>Ca_<0.5>, Ca, Ca_<0.5>La_<0.5>, La) and measured their DC magnetization, AC susceptibility, specific heat, and resistivity, in order to investigate the effects of the hetero-valent substitution. A broad peak in the DC magnetization around 200K was observed only in CaCu_3Ru_4O_<12>, suggesting the Kondo effect due to localized Cu^<2+> ions. However, the electronic specific heat coefficients γ exhibit large values not only for CaCu_3Ru_4O_<12> but also for all the other samples. Moreover, the Wilson ratio and the Kadowaki-Woods ratio of our samples are all similar to the values of other heavy-fermion compounds. These results question the Kondo effect as the dominant origin of the mass enhancement, and rather indicate the importance of correlations among itinerant Ru electrons.
社団法人日本物理学会の論文
2009-02-15