Low temperature magnetic properties of U_1-xPr_xAl ₂

The low temperature properties of U_1-xPr_xAl ₂ (0<x<0.15) were studied by susceptibility and specific heat measurements down to 100 mK, focusing attention on the mechanisms of spin fluctuations. The low temperature behavior of C/T has been explained by the paramagnon theory for low energy excitations with long wavelengths. However, the spin fluctuations in wider temperature ranges in UAl₂ seems to be more complicted as suggested by a recent nuclear magnetic resonance experiment. In UAl₂, the susceptibility and the specific heat show two different temperature ranges, above and below about 50 K where there is a crossover from a single impurity Kondo regime to a low temperature coherent Kondo state. On the other hand, the enormous increase of γ with x in U_1-xPr _xAl₂ seems to be a consequence of the static f and d-band structures near the Fermi level.