Structure and Physical Properties New Heavy Fermion Systems -Amorphous Cerium Alloys-

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In Ce-based alloys, the f electrons mix with s and p electrons and their strong correlation make the effective mass of conduction electrons very heavy. In this project, we have studied X-ray diffraction, lowtemperature specific heat, magnetic susceptibility, electrical resistivity, magnetoresistance, thermoelectric power and X-ray photo electron spectroscopy of amorphous (a-) Ce alloys. We obtained the following results. 1) The electronic specific heat coefficient, gamma, is much larger in a-Ce-Cu, a-Ce-Si and a-Ce-Ru alloys than in a-La alloys, demonstrating the importance of 4f electrons in the heavy electron systems. 2) In the a-Ce-Cu alloys, the random structure disturb the electron correlation to result in an impurity or incoherent Kondo (IK) state. 3) In the a-Ce-Si alloys, a rather strong Kondo effect displays a signature of a coherent Kondo (CK) state, but still an IK state is realized due to their random structures. 4) In the a-Ce-Ru alloys, the mixing of 4f and conduction electrons and their correlation are so strong that a CK state and a superconducting state are realized. 5) The interatomic distance between Ce atoms decreases with increasing Ce concentration, while those for Ce-Cu, Ce-Si and Ce-Ru are insensitive to the alloy concentrations. The coordination numbers around Ce atoms are smaller in the amorphous states than in their crystalline counterparts. 6) Valence and core electron spectra indicate that the mixing of 4f and conduction electrons is enhanced in order, the a-Ce-Cu, a-Ce-Si and a-Ce-Ru alloys. 7) The physical properties of the a-Ce-Ni alloys produced by vapor deposition and liquid quenching are quite different, suggesting that the degree of randomness depends on preparation methods.