Inelastic magnetic neutron scattering in CeT2Si2(T=Au, Pd, Ru or Pt): crystal fields and quasi-elastic scattering

Abstract

The authors have measured the inelastic magnetic scattering of neutrons in polycrystalline samples of CeT2Si2 (T=Au, Pd, Ru or Pt) for energy transfers in the range 0-40 meV at several temperatures. Quasi-elastic scattering as well as scattering from crystal field levels is observed. For CeAu2Si2 at T=8 K a crystal field excitation is observed at 20.5 meV with a linewidth equal to the instrumental resolution. For CePd2Si2 a crystal field is observed at 21 MeV whose linewidth (10 meV) is much larger than the resolution. Below TN=10 K a magnon is observed at 2.5 meV; for T equal to 12 K and 100 K quasi-elastic scattering is observed with linewidths Gamma QE of 0.76 meV and 2.56 meV, respectively. For CeRu2Si2 quasielastic scattering is observed at T equal to 5 K, 50 K and 100 K with linewidths of 1.78 meV, 2.07 meV and 2.52 meV, respectively. No crystal field excitations are observed although the known transport behaviour implies their existence. The data for CePt2Si2 can be fitted to the quasi-elastic law at T=5, 50 and 100 K ( Gamma QE=15, 10.7 and 9.9 meV); however, they are also consistent with a spectrum consisting of a quasi-elastic line with a smaller linewidth plus a broadened crystal field at a higher energy. In the discussion, they show that the measured linewidths yield Kondo temperatures (kBTK- Gamma QE) in good agreement with the known thermodynamic properties of these compounds and confirm that spin fluctuation effects increase in the sequence T identical to Au, Pd, Cu, Ru, Pt. They find that CePd2Si2 has nearly the same quasi-elastic linewidth and normal state transport behaviour as the heavy-fermion superconductor CeCu2Si2. They argue that stronger ferromagnetic correlations in CePd2Si2 stabilise the moment and allow for antiferromagnetism in the ground state.