NMR studies of actinide dioxides

O17 NMR measurements have been performed on a series of the actinide dioxides, UO2, NpO2 and PuO2. Although the O17 NMR spectra in these materials are similar at higher temperatures, the low-temperature spectra present are significantly different. In UO2 we have observed a wide spectrum, forming a rectangular shape below TN=30TN=30 K. In NpO2, on the other hand, the spectra broaden rather gradually and exhibit a two-peak structure below T0=26T0=26 K. In PuO2, neither spectrum broadening nor splitting has been observed. We show that these NMR spectra clearly indicate the different nature of the low-temperature magnetic ground states in these actinide compounds.