Non-Fermi-liquid behavior ofYbCu5−xAlx

A valency change in ${\mathrm{YbCu}}_{5-x}{\mathrm{Al}}_x$ from $\nu \approx 2.2(x=0\mathrm{})\mathrm{}$ to $\nu =3\mathrm{}(x=2\mathrm{})\mathrm{}$ causes a magnetic instability near a critical concentration $x_{\mathrm{cr}}\approx \mathrm{1.5.}$ Alloys in the vicinity of $x_{\mathrm{cr}}$ exhibit typical non-Fermi-liquid properties like a negative logarithmic contribution to the specific heat or substantial deviations of the electrical resistivity from a $T^2$ behavior. Both pressure and alloying in this series bring about a strong reduction of the Kondo temperature $T_K;$ the crystal-field interaction and the interatomic exchange gain therefore importance and magnetic order becomes possible beyond $x_{\mathrm{cr}}.$