Magnetic, Transport, and Nuclear-Magnetic-Resonance Properties ofU1−xPuxAl2

Magnetic-susceptibility, electrical-resistivity, and ${}_{}{}^{27}{}_{}{}^{}\mathrm{Al}$ Knight-shift and spin-lattice-relaxation results on the pseudobinary cubic Laves phase compounds ${\mathrm{U}}_{1-x}{\mathrm{Pu}}_x{\mathrm{Al}}_2$ are presented. Samples in the annealed and in the self-irradiation-damaged state were studied. The results are consistent with spin fluctuations of the $5f$ electron state associated with the actinide ions. The strength of the coupling between the $s$-wave conduction electrons at the Fermi energy and the $5f$ state is found to increase rapidly with plutonium concentration. In atomically well ordered Pu${\mathrm{Al}}_2$ the coherence of the $s-f$ hybridization is destroyed by spin-fluctuation scattering above 10 °K. The $5f$ states behave as incoherent virtual bound states centered at the Fermi level in damaged Pu${\mathrm{Al}}_2$ and the Pu-rich alloys. Antiferromagnetic order is found at 6 °K for ${\mathrm{U}}_{0.7}$ ${\mathrm{Pu}}_{0.3}$ ${\mathrm{Al}}_2$.