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, CeCu6−xAux has become a prototype heavy-fermion (HF) system where, starting from not magnetically ordered CeCu6, Au doping introduces long-range incommensurate antiferromagnetism for x > x c ≈ 0.1 . At the critical concentration x c 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 x c . While most rare-earth HF compounds have a tendency towards antiferromagnetic order, CeSi1.81 presents one of the comparatively few cases exhibiting ferromagnetic order below T c = 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, μ S , which vanishes around p ≈ 13 kbar.