69Ga NMR and magnetic susceptibility in δ-phase of Pu1−xGax (x=0.05, x=0.08) alloys

Abstract 69Ga nuclear magnetic resonance spectra, line shifts (69K) and nuclear spin-lattice relaxation rate 69 T 1 - 1 have been measured in the 20 years aged Pu0.95Ga0.05 and in fresh prepared Pu0.92Ga0.08 alloys, stabilized δ-phase, at magnetic field of 9.4 T in the temperature range (10–500) K. The line shift and 69 T 1 - 1 are determined correspondingly by the static and fluctuating-in-time parts of the local magnetic field that originates in transferred hyperfine coupling the Ga nuclear spin with the nearest f-electron environment of more magnetic Pu. Temperature behavior of the resonance properties is found the same in fresh Pu0.92Ga0.08 and aged Pu0.95Ga0.05 alloy. The NMR results are in favor that δ-phase of Pu1−xGax alloys represents at T > 200 K the Kondo lattice, in which the localized electronic spins fluctuate independently from each other without any macroscopic coherence. The coherent state like in heavy-fermion liquids emerges in Pu0.95Ga0.05 below T∗ = 200 K. A little bit higher estimate of crossover temperature T∗ = 250 K was founded for Pu0.92Ga0.08.