Inelastic neutron scattering study of cerium heavy fermion compounds

We will review inelastic neutron scattering experiments performed on single crystals of the heavy fermion compounds CeRu 2Si 2 and CeCu 6. At high temperatures, the magnetic scattering can be described by a single quasi-elastic Lorentzian peak. At low temperatures antiferro and incommensurate magnetic correlations develop below 70 and 10 K in CeRu 2Si 2 and CeCu 6, respectively; the associated wave vectors are k 1 = (0.3, 0, 0) and k 2 = (0.3, 0.3, 0)for CeRu 2Si 2 and k 1 = (0, 0, 1) and k 1 = (0, 0, 1) and k 2 = (0.85, 0, 0) for CeCu 6. These magnetic correlations are destroyed by a magnetic field applied along the easy axis ( H c ≈ 25 kOe for CeCu 6, H c ≈ 83 kOe for CeRu 2Si 2). These high field experiments allow us to establish that in both compounds, at low T and H = 0, the magnetic scattering is the superposition of two contributions: i) a q-independent (single site) quasi-elastic contribution of Lorentzian type, slowly decreasing at high field, ii) a strongly peaked inelastic contribution associated with magnetic correlations, centered at a finite energy ħω 0 with characteristic energy width Γ ≈ ħω 0 ≈ 1.2 meV and 0.2 meV for CeRu 2Si 2 and CeCu 6, respectively.