NMR evidence for higher-order multipole order parameters in NpO2.
We report a microscopic investigation of multipolar order parameters in the ordered state of NpO2 conducted via 17O NMR on a single crystal. From the angular dependence of hyperfine fields at 17O nuclei, we have obtained clear evidence for the appearance of field-induced antiferro-octupolar as well as field-induced antiferro-dipolar moments below T0 = 26 K. We have also observed oscillatory spin-echo decay, which is well understood in terms of small electric field gradients created by antiferro-quadrupolar ordering. This reveals that the quadrupolar order parameter is directly observable by means of NMR. The present NMR studies provide definitive support for a proposed longitudinal triple-q type octupolar-quadrupolar ordering model for NpO2.
Tokunaga
Y
Y
ASRC, Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan.
Aoki
D
D
Homma
Y
Y
Kambe
S
S
Sakai
H
H
Ikeda
S
S
Fujimoto
T
T
Walstedt
R E
RE
Yasuoka
H
H
Yamamoto
E
E
Nakamura
A
A
Shiokawa
Y
Y