UC Irvine

We have measured the momentum and energy dependence of the spin fluctuations in the low-temperature mixed-valent state and the high-temperature integral-valent state of (Formula presented), using flux-grown single crystals and a triple axis spectrometer. The magnetic scattering can be fit with a Lorentzian power spectrum, with positions and halfwidths equal (Formula presented)=2.3 meV and (Formula presented)=1.8 meV in the high-temperature state at 50 K and (Formula presented)=40.2 meV and (Formula presented)=12.3 meV in the low-temperature state at 20 K. Within the experimental uncertainties, the line shape as a function of energy transfer (i.e., the power spectrum) does not depend on momentum transfer Q. The static susceptibility χ(Q) is no more than 10% larger at the zone boundary than at zone center for the [1,0,0] direction. The results compare reasonably well to the predictions of the Anderson impurity model and to earlier measurements on polycrystalline samples. © 1997 The American Physical Society.