Impurity effects on the low-temperature properties of UAl₂

We have measured the magnetization of pure UAl₂ below 1 K down to 0.1 K and the effects of impurities on the susceptibility and specific heat in the temperature range 2-370 K for the susceptibility and 1.5-20 K for the specific heat. The magnetization of UAl₂ shows a slight upturn in the curvature below 1 K with respect to the applied magnetic field. This behavior is quite similar to that of CeRu₂Si₂ below the critical field of the metamagnetic-like jump. Silicon impurities suppress the enhancement of the electronic specific heat coefficient, in contrast with the case of praseodymium.