17O NMR study in (Pu0.91Am0.09)O2

In order to investigate the magnetic properties of Am4+ ions in the cubic fluorite structure, we have performed 17O NMR measurements on (Pu0.91Am0.09)O2. We have observed a temperature-dependent 17O NMR line broadening induced by classical dipolar hyperfine fields from the Am 5f moments. From NMR line simulations, the effective moment of the Am moments has been estimated to be μ eff = 1.38 μ B / Am . This value is comparable with μ eff = 1.32 or 1.53 μ B / Am reported for AmO2. We have also carried out nuclear relaxation measurements for 17O nuclei. The magnetization recovery has been found to exhibit a nonexponential time dependence with an exponent β ∼ 0.5 . This result is well understood in terms of the nuclear relaxation mechanism induced by the Am 5f moment fluctuations via dipolar hyperfine fields.