Structural, magnetic, transport and thermal properties of YbCu5-xAux alloys with Au concentration between the limit of structural stability of AuBe5 type at x = 0.4 up to x = 0.7 are reported. The outstanding features of this system are: i) the const
ant and record high values of Cm /T 7J/molK^2 below a characteristic temperature T*, ranging between 150 mK and 350 mK. ii) A power law thermal dependence dependence Cm/T(T>T*)=A/T^q, with q = 1.3 +/- 0.1, and iii) an arising incoherent electronic scattering observed in the resistivity at T < 1K for x < 0.6 despite the fact that Yb magnetic atoms are placed in a lattice. Magnetic frustration, originated in the tetrahedral distribution of Yb atoms, appears as the responsible of the exotic behavior of this system.
The non-Fermi liquid system (NFL) YbCu_(5-x)Al_(x) (x = 1.3 - 1.75) has been investigated in hetero- as well as homo-contact arrangement in magnetic fields up to 22.5 T. The observed dV/dI(V) characteristics reveal asymmetry in hetero-contact arrange
ment and do not agree with the model of thermal contact heating, at least close to zero-bias voltage. In the case of a hetero-contact arrangement we have observed a maximum at only one voltage polarity at about 1.3 mV (for x = 1.5), which asymmetry is suppressed in an applied magnetic field. This behavior is connected with NFL properties of studied compounds.
