27Al nuclear magnetic relaxation studies of spin fluctuation in UAl2

The microscopic magnetic properties of UAl2 have been investigated by 27Al NMR from 1.5 to 500 K. The observed T-dependence of 1/T1 indicates a cross-over from higher-T local-moment-like behavior to lower-T Fermi-liquid behavior with a characteristic spin fluctuation (SF) temperature T* ≅ 100 K. Above T*, a characteristic energy-scale of the SF is found to be large and to increase almost linearly with temperature, indicating both strong hybridization between 5f and conduction electrons and the dominance of single-site dynamics in the U-moment relaxation at higher temperatures. Below T*, a development of significant q-dependence of the SF with decreasing temperature is concluded from the analysis of T1 in connection with previous neutron measurements. Based on the observed proportionality between an increase of 1/(T1T) and that of χ below 40 K, the onset of a ferromagnetic correlation, in addition to an only weakly q-dependent single-site fluctuation with a larger energy-scale, is suggested at lower temperatures. (author)