NMR study of magnetic fluctuations in 115 actinide compounds

We report NMR measurements in isostructural compounds (HoCoGa5HoCoGa5: 115 type) AnTGa5AnTGa5 (An: U, Np and Pu, T: Fe, Co and Pt) with different ground states (paramagnet, antiferromagnet and superconductor) using single crystal samples. The electrical field gradient at the Ga and Co sites are similar in all compounds, indicating that the charge distribution around these sites is determined mainly by intra-atomic orbitals. In contrast, the hyperfine coupling constants at the Ga and Co sites depend on the compounds considerably. Since the hyperfine coupling at the ligand sites is a transferred hyperfine coupling due to hybridization between 5f and ligand orbitals, it is natural that the hyperfine coupling constant depends on the 5f electronic states. Spin–lattice relaxation rates (1/T1)(1/T1) in the paramagnetic state show more drastic differences between the compounds. In the antiferromagnets UPtGa5UPtGa5, NpFeGa5NpFeGa5 and NpCoGa5NpCoGa5, 1/T1T1/T1T shows a Curie–Weiss behavior at high temperatures, indicating a strong localized character. By contrast, in the paramagnet UFeGa5UFeGa51/T1T1/T1T is small and almost independent of T  , indicating an ordinary metallic state with weak exchange enhancement. Finally, in the superconductor PuRhGa5PuRhGa5 the magnitude of 1/T1T1/T1T lies between those of the antiferromagnets and the paramagnet.