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Discovery of Superconducting Neptunium CompoundMay. 25, 2007Dr. D. Aoki and Prof. Y. Shiokawa (Tohoku University), Dr. Y. Haga (Japan Atomic Energy Agency) and Prof. Y. Onuki (Osaka University) found a new neptunium compound NpPd5Al2, the first neptunium-based superconductor. Neptunium (Np) is located between uranium (U) and plutonium (Pu) in the periodic table. Although the handling of 'transuranium elements' including Np is very difficult because of its radioactivity, their fundamental properties have attracted attentions recently. Superconductivity is one of the universal phenomena which many metals show at low temperatures. It is also important in industrial applications because the electrical current flows without loss in the superconducting state. However, the application of magnetic field easily destroys superconductivity. Since most of neptunium compounds show strong magnetic properties, it has been believed that superconductivity is not likely to occur. The compound NpPd5Al2 was synthesized in the present study for the first time. The x-ray diffraction experiments revealed the tetragonal crystal structure. The superconducting transition temperature is 5 K (-268°). This compound exhibits novel characteristics as follow: (1) The superconducting upper critical field where the superconductivity is destroyed is quite large, 15 T (500,000 times the earth magnetic field). (2) Superconductivity is realized in the presence of magnetism of neptunium. (3) Characteristic features are similar to those of the high-Tc cuprate superconductors. The present discovery is outstanding because it has broken the consensus that neptunium compound will not superconductE It also suggests that further novel properties can be found by investigating transuranium elements and their compounds. The understanding of the superconducting mechanism in such magnetic compounds is expected to promote the development of other superconducting as well as magnetic materials. This result will be published as a Letter in the Journal of the Physical Society of Japan in the June issue. It was also selected as one of the "Papers of Editors' Choice" of this journal.  |
