In this contribution, after presenting the existing theoretical models, we discuss the evidence for non-Fermi liquid behaviour in Yb(Cu1-xSix)2-y that have been investigated for the last years in our Institute. The alloys crystallize in the hexagonal AlB2 type structure and exhibit a dramatic change in the electronic properties upon change of the electron concentration. Undoped YbSi2-y is an intermediate valent system, whereas the doping with 10% Cu ensures A(T) ??Tn, A(T) ??T and Cp ??T-1/2 dependences. Comparison of the data with the Griffiths phase model shows that this model can describe some of the observed results. We present also a study of the Hall effect. The Hall coefficient at 7 T is found to follow a lnT dependence below 10 K, thus showing the behaviour opposite to that in Fermi-liquid heavy-fermion systems.
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Magnetic phase diagram of the URhxRu1-xGe solid solutions has been reinvestigated by means of dc-magnetization, ac-susceptibility and electrical resistivity. We confirm ferromagnetic order only in alloys with x ??0.2. For a limited range of concentrations x between 0.3 and 0.35, we found features characteristic of short-range magnetic interactions. For compositions close to x = 0.4, non-Fermi liquid signature is observed in the low temperature resistivity. Thus, we report on the evolution of non Fermiliquid behaviour at a magnetic-nonmagnetic border, neighbouring with the region of the short-range interactions.
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