Q-dependence of the spin fluctuations in the intermediate valence compound CePd₃

We report inelastic neutron scattering experiments on a single crystal of the intermediate valence compound CePd₃. At 300 K the magnetic scattering is quasielastic, with half-width Γ=23 meV, and is independent of momentum transfer Q. At low temperature, the Q-averaged magnetic spectrum is inelastic, exhibiting a broad peak centered near E_max=55 meV. These results, together with the temperature dependence of the susceptibility, 4f occupation number, and specific heat, can be fit by the Kondo/Anderson impurity model. The low temperature scattering near E_max, however, shows significant variations with Q, reflecting the coherence of the 4f lattice. The intensity is maximal at (1/2, 1/2, 0), intermediate at (1/2, 0, 0) and (0, 0,0), and weak at (1/2, 1/2, 1/2). We discuss this Q-dependence in terms of current ideas about coherence in heavy fermion systems.