Effects of structure-disorder on electron-correlation in Ce-based amorphous alloys

The amorphous Ce based alloys, Ce-Cu, Ce-Si and Ce-Ru produced by sputtering show several heavy fermion behaviors at low temperatures. The electronic specific heat coefficient estimated from the specific heat above 10 K is more than hundred times larger than those of simple metals and it rapidly increases below 5 K (a heavy fermion behavior). The electrical resistivity is large due to disorder scattering and its temperature dependence displays -logT dependence at low temperatures (an incoherent or impurity Kondo effect). However, it show roughly AT(2) (A>0) dependence and positive magnetoresistance in the Ce-Ru amorphous alloy whose crystalline counter part has a very high Kondo temperature (a coherent Kondo effect). The short range structures of the Ce-Cu and Ce-Si amorphous alloys are chemically ordered ones, resembling their crystalline counterparts, while that of the Ce-Ru amorphous alloy is a disordered one, different from the crystalline counterpart. These results demonstrate that the heavy fermion characteristics are depressed but not smeared out even in random alloys. Moreover, the electron correlation effects observed in the amorphous Ce-Ni alloys indicate that the degree of randomness is much higher in the vapor-quenched state than in the liquid quenched state.