Noncrossing approximation solution of the anisotropic Anderson impurity model

The thermodynamic and magnetic properties of a single impurity Anderson model that describes Ce in an environment with hexagonal symmetry is treated within the noncrossing approximation. It is found that the properties of the system at temperatures larger than the crystal field splitting are described by a Kondo temperature of the sixfold-degenerate spin-orbit multiplet and at low temperatures by a highly renormalized Kondo temperature of the crystal field ground state. The inelastic neutron scattering spectra exhibits a quasielastic and inelastic component. The results are compared with the concentrated heavy-fermion compound CeAl3. The system is well described by the single-impurity Anderson model at temperatures above 1 K, with the crystal field scheme determined by Goremychkin et al. from inelastic neutron scattering experiments. The excellent agreement may be due to the small variation of the f occupation number with temperature in heavy-fermion systems. However, the single-impurity model fails to describe the peak in the ratio C(T)/T found in earlier experiments. Therefore, it is concluded that this peak is either due to the coherence of the lattice or due to magnetic interactions that may be responsible for spin-glass-like ordering.