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Novel Magnetic Ordering in Neptunium Dioxide NpO2
-Experimental confirmation of magnetic octupolar ordering-

Dec. 19, 2006

·Abstract

Japan Atomic Energy Agency (JAEA), in collaboration with the Institute of Materials Research in Tohoku University (IMR Tohoku Univ.), has initiated the first NMR study of the unconventional, low-temperature electronic state of Neptunium dioxide NpO2, which has been unsolved for more than 50 years. The experiments have discovered the occurrence of a novel type of magnetic ordering associated with the octupole moment of the Np 5f-electrons. This study has been done by Dr. Yo Tokunaga, Dr. Shinsaku Kambe (JAEA), Dr. Yoshiya Homma, Dr. Dai Aoki, Prof. Yoshinobu Shiokawa (IMR Tohoku Univ.) and colleagues.

The phase transition at low temperature in NpO2 was originally discovered in 1953. Since this discovery, however, it has remained a most-lasting mystery in the physics of actinide compounds. The present finding reveals that multipolar degrees of freedom, characteristic of f-electrons, bring rich and complex physics to actinide materials. The study of actinide compounds will lead to the understanding of their unconventional superconducting properties, as well as their novel phase transitions associated with multipoles.

This result has been published in PHYSICAL REVIEW LETTERS 97, 257601 (2006).

•Novel Magnetic Ordering in Neptunium Dioxide NpO2 (PDF)

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