Rare-earth intermetallic compounds at a magnetic instability

Rare-earth intermetallic alloys and compounds, in particular those with Ce or Yb, are often close to a magnetic instability. In particular, CeCu _6-xAu_x has become a prototype heavy-fermion (HF) system where, starting from not magnetically ordered CeCu₆, Au doping introduces long-range incommensurate antiferromagnetism for x>xc≈0.1. At the critical concentration xc the system experiences a quantum phase transition (QPT). Here, the unusual magnetic fluctuations probed by inelastic neutron scattering lead to non-Fermi-liquid behavior, i.e. to anomalous low-temperature thermodynamic and transport properties. Hall-effect measurements delineate the "bandstructure" of heavy fermions across the critical concentration xc. While most rare-earth HF compounds have a tendency towards antiferromagnetic order, CeSi_1.81 presents one of the comparatively few cases exhibiting ferromagnetic order below Tc=9.5 K. In a search for a ferromagnetic QPT in HF metals, we have studied the pressure dependence of the magnetization and the spontaneously ordered magnetic moment, μS, which vanishes around p≈13 kbar.