Solid-state NMR study of actinide dioxides

Tokunaga, Yo  ; Sakai, Hironori   ; Kambe, Shinsaku  ; Chudo, Hiroyuki ; Osaka, Masahiko  ; Miwa, Shuhei  ; Nishi, Tsuyoshi; Nakada, Masami  ; Ito, Akinori; Homma, Yoshiya*

Besides the importance of AnO series (An; U, Np, Pu, Am) as a nuclear fuel, the magnetic properties of these compounds at low temperatures are particularly interesting. Their surprisingly varied physical properties continue to be of interest for both theory and experiment. In this study, we have performed NMR studies for the series of actinide dioxides. On the basis of O-NMR studies, exotic magnetic orderings associated with multipole degrees of freedom on 5 electrons have been identified in UO (dipolar + quadrupolar ordering) and NpO (octupolar + quadrupolar ordering), in contrast with the non-magnetic ground state of PuO. In AmO, our O-NMR data provide the first microscopic evidence for a phase transition as a bulk property in this system.