HEAVY-FERMION BEHAVIOR IN THE TH2ZN17-TYPE PSEUDOBINARY SYSTEMS U-2(CU, M)(17) (M=AL OR GA)

Several pseudobinary compositions in the systems U-2(CuxAl1-x)(17) and U-2(CuxGa1-x)(17) have been prepared for samples with x approximate t o 0.45-0.7 and were found to crystallize in the rhombohedral Th2Zn17-t ype structure (space group R (3) over bar m), with rather uniform latt ice parameters (compositions out of these x ranges adopt other crystal structures and/or are multiphase). All compositions, studied by elect rical-resistivity and DC-susceptibility measurements in the temperatur e range 4.2-300 K, are metallic, and do not order magnetically in the entire range. The electrical resistivity is rather flat, but with a sm all decrease (Kondo-type) for the Cu-poorer samples. Above 50 K the ma gnetic susceptibility follows the Curie-Weiss law, with negative(- 96- - 50 K) paramagnetic Curie temperatures and effective magnetic moment s close to 3 mu(B). Specific-heat measurements down to 1.1 K yield at this temperature a C/T ratio of 550-1000 mJ K-2 mol(-1), thereby indic ating the heavy-fermion behaviour in all these compositions.