NMR study of the electronic spin fluctuation in U-based systems with heavy fermion properties

Abstract

We report NMR measurements on several U-based compounds exhibiting possible heavy fermion behavior. An operational method for a quantitative evaluation of the electronic spin fluctuation rate is proposed; the consistency of which is checked from the spin fluctuation rate, Γ NMR, deduced from T 1 measurements on both 29Si and 195Pt nuclei in UPT 2Si 2. This al lows us a systematic determination of spin fluctuation rate in UBe 13, URu 2Si 2 and UInAu 2. It is found in the latter compounds that Γ NMR follows a √ T law at high temperatures similar to that observed in Ce (Yb) heavy fermion compounds. The low temperature behavior differs in the three compounds. UInAu 2 is found to order magnetically. In URu 2Si 2 we confirm the occurrence of a spin wave with a gap opening involving only a part of 5f electrons. In UBe 13, which is known to present heavy fermion properties, the low Γ values by NMR are consistent with specific heat results but in strong qualitative disagreement with inelastic neutron scattering experiments. A further speculation concerning the electronic response in UBe 13 is presented which could explain this disagreement.