We report a microscopic investigation of multipolar order parameters in the ordered state of NpO2 conducted via O17 NMR on a single crystal. From the angular dependence of hyperfine fields at O17 nuclei, we have obtained clear evidence for the appearance of field-induced antiferro-octupolar as well as field-induced antiferro-dipolar moments below T0=26K. 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.
ASJC Scopus subject areas
- Physics and Astronomy(all)