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日時 平成16年(2004年)9月21日(火)17:00〜18:00
場所 理学研究科H棟3階 コミュニケーションスペース
講師 Dr. GRIVEAU Jean-Christoph
(Institute for Transuranium Elements Karlsruhe, Germany)
題目 Magnetic Properties of Transuranium Compounds
概要 Due to their high radio toxicity and self heating effect, transport properties of transuraniums compounds (Np, Pu, Am, Cm) have been poorly known especially at low temperature (T < 1 K). Pressure studies have been achieved mainly on the crystallographic structure to observe localization-delocalisation of the 5f electrons. We developed recently high pressure resistivity facilities for measurement down to 300 mK and up to 30 GPa. Np, Pu and Am-115 systems compounds have been studied. The dramatic change of superconducting state developing in Am metal at temperature lower than 2 K has set a new challenge to overcome the technical difficulties imposed by the manipulation of these of materials (radio toxicity and heating power of 6.3 mW/g for 243Am). Here we report the main technical advances for the studies of transuranium compounds. We present the Am Tc(p) diagram under 1 K and critical field Hc with pressure assuming a possible change of superconductivity from type I to type II. Pressure results on the recent discovered plutonium based superconductors PuCoGa5 [4] and PuRhGa5 indicate a surprising important robustness vs. mechanical constraints reinforcing the d-wave superconductivity scenario as NQR results stress it. But their Non Fermi Liquid (r~T1.34) is still observed up to pressure close to 20 GPa. Their Neptunium counterparts present a clear magnetism (AFM) reinforced under pressure in the case of NpCoGa5. Finally, recent study of other AnCoGa5 indicate a non magnetic ground state (An=U, Am).

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