NMR evidence for triple- multipole structure in NpO

Tokunaga, Yo  ; Homma, Yoshiya*; Kambe, Shinsaku  ; Aoki, Dai*; Sakai, Hironori   ; Yamamoto, Etsuji  ; Nakamura, Akio; Shiokawa, Yoshinobu; Walstedt, R. E.; Yasuoka, Hiroshi

In order to elucidate the nature of the exotic ordered phase of NpO below = 26 K, we have initiated the first O-NMR measurements on this system. From the O-NMR spectrum, the occurrence of two inequivalent oxygen sites has been confirmed below . It has also been shown that the characteristic features of the hyperfine interaction at the oxygen sites are well explained by invoking a hyperfine interaction with field-induced antiferromagnetic moments which appear as a result of the triple- antiferro-quadrupolar order. The NMR findings strongly support the occurrence of the longitudinal triple- multipole structure in NpO.