Non-Fermi-liquid behavior in a heavy-fermion alloy at a magnetic instability

The specific heat C and electrical resistivity ρ of the heavy-fermion alloy ${\mathrm{CeCu}}_{5.9}$ ${\mathrm{Au}}_{0.1}$ exhibit non-Fermi-liquid behavior well below 1 K, i.e., C/T∝-ln(T/${\mathit{T}}_0$) and ρ=${\mathrm{\rho }}_0$+A’T, over more than a decade in temperature T. The magnetic susceptibility χ measured in 0.1 T shows a cusp for T→0. This behavior is attributed to the proximity to magnetic order: In contrast to ${\mathrm{CeCu}}_6$, ${\mathrm{CeCu}}_{6\mathrm{-}\mathit{x}}$ ${\mathrm{Au}}_{\mathit{x}}$ alloys show long-range antiferromagnetic order, with ${\mathit{T}}_{\mathit{N}}$→0 for ${\mathit{x}}_{\mathit{c}}$=0.1. Hence ${\mathrm{CeCu}}_{5.9}$ ${\mathrm{Au}}_{0.1}$ is at the edge of a zero-temperature quantum phase transition. In a large magnetic field (B≥3 T) Fermi-liquid behavior is recovered.